Here today, gone tomorrow—your libido can be puzzling, to say the least. But that ebb and flow is completely natural, says Lauren Streicher, MD, a clinical associate professor of obstetrics and gynecology at Northwestern Memorial Hospital in Chicago: "All women go through periods when they feel especially frisky, as well as times when they just seem to have lost their mojo."

Read on to learn about the many reasons your libido may come and go, and how to find it when you miss it. Curious about aphrodisiacs? We've got those too, from strawberries to Savasana.

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The brain is your biggest sex organ

Your brain is where the spark starts. Five of the most important areas:

Ventral striatum: A 2012 fMRI study found that this area lights up when you see something lust-inducing (like, say, Idris Elba).

Amygdala: Some research suggests that your sex drive may be proportional to the size of your amygdala, the almond-shaped emotion center of your brain.

Hypothalamus: When you experience something rewarding (such as a great kiss), this part of the brain produces dopamine, a neurotransmitter that's critical for pleasure and motivation.

Cerebral cortex: The brain's outer layer of gray matter is responsible for higher functions, including thoughts about sex. It triggers a chain reaction that ultimately leads to the production of sex hormones.

Pituitary: This gland secretes luteinizing hormone, which stimulates your ovaries to produce estrogen. It also makes the "mothering" hormone prolactin—typically during pregnancy and breastfeeding—which lowers libido.

Desire may increase with age

A 2010 study showed that as a woman's fertility wanes in her 30s and 40s, her sexual fantasies become more frequent and steamier (!) and her sex drive becomes stronger overall. Researchers suspect it's an evolutionary trick, designed to up your odds of procreating by encouraging you to do the deed more often. Life circumstances play a role, too, said Dr. Streicher, who wrote “Sex Rx: Hormones, Health, and Your Best Sex Ever.”

"You're more comfortable with your partner and less worried about contraception," she explained.

Of course, there's also the confidence that comes with age: A large 2015 survey discovered that most women who find sex more pleasurable as they get older credit their improved body image. After all, there's nothing like feeling sexy to put you in the mood.

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The pink pill has perks—and risks

Last year, the FDA approved Addyi, the first-ever Rx sex drug for women. Unlike its male counterpart, Viagra, which works by improving blood flow to the genital region, Addyi is thought to boost desire by altering the balance of neurotransmitters (like serotonin and dopamine) in a woman's brain. Alas, the daily pill, approved for premenopausal women, has a range of unsexy possible side effects—including nausea, dizziness, and sleepiness—and alcohol isn't allowed while you're on it. For postmenopausal women, there are other options that may help increase libido, such as Rx testosterone cream (taken off-label) or hormone therapy.

Stress kills your sex drive

"Lab research has shown that women experiencing stress, as evidenced by increased cortisol, have less response to erotic cues," said Sheryl Kingsberg, PhD, chief of the division of behavioral medicine at University Hospitals Case Medical Center in Cleveland. "Stress is a tremendous distracter," she explained. "It takes away from your ability to focus and be fully present."

But distraction isn't the only factor. Tension can take a toll on a relationship, too. It's not surprising that a Monmouth University study found that couples placed in stressful situations behaved more poorly to each other.

"Disdain and anger are definitely not aphrodisiacs," Streicher said.

Stress can also prevent you from sleeping enough, leaving you too pooped to get busy. The good news: A 2015 study revealed that just one extra hour of shut-eye a night leads to a 14 percent boost in libido.

RELATED: 13 Ways to Beat Stress in 15 Minutes or Less

Some medications can affect sex drive

Some meds can make your sex drive take a nosedive. If you suspect that any of these drugs are to blame, ask your doctor about switching to an alternative.

Birth control pills: They lower levels of active estrogen and testosterone, Streicher explained. Progestin-only pills and IUDs are just as effective at preventing pregnancy and don't tamp down libido.

SSRIS: These antidepressants are known libido busters, but a different type of drug—bupropion—is less likely to affect sex drive.

Blood pressure meds: In a French study, 41 percent of postmenopausal women taking these drugs reported lowered sexual desire. Beta-blockers, often used to treat hypertension, are common culprits. You may want to consider trying valsartan, another type of blood pressure med that has actually been shown to boost libido.

Antihistamines: These drugs tend to dry out mucus-producing cells everywhere in the body, including the vagina, Streicher said. But the side effect is less common with second-generation antihistamines (like Zyrtec and Claritin). There are nondrug allergy treatments as well, such as immunotherapy shots and pills.

Yoga can help

Can Downward Dog really up your libido? When researchers had women do an hour of yoga daily, they found that nearly 75 percent were more satisfied with their sex life after 12 weeks. It makes sense, given the relaxing effects of yoga.

"By facilitating deeper breathing and calming the autonomic nervous system, yoga can help direct more blood flow to the pelvic organs," said Dr. Timothy McCall, author of “Yoga as Medicine.”

So we asked yoga teacher Kate Hanley, author of “A Year of Daily Calm,” for three lust-stimulating poses. Her top picks: Cobra (it might trigger a surge in testosterone, according to a 2004 study), Extended Side Angle (it stretches out your pelvis), and Savasana (it quiets the chatter in your mind). 

RELATED: Best Yoga Poses for Your Trouble Spots

If your libido is MIA, see your MD

It's tempting to dismiss a dwindling sex drive, chalking it up to a hectic month (or year)—but any significant drop that lasts more than a few weeks is worth getting checked out, Streicher said.

"You may have an underlying medical condition," she explained.

At the top of the list of possibilities: hypothyroidism, which can affect the production of sex hormones, and depression, which interferes with feel-good neurotransmitters. The problem could also be hypertension or even undiagnosed type 2 diabetes. The fact is, virtually any chronic condition can wreak havoc on your libido, Streicher said, because "your body has little energy left for anything else." If you've lost your sex drive, see your doc, she urges. The right treatment could get you back on track.

Certain foods can help

Spice things up! Health's nutritionist, Cynthia Sass, RD, serves up five tasty aphrodisiacs. 

Berries: Blueberries and strawberries both contain an antioxidant called anthocyanin, which boosts circulation, creating a "natural Viagra effect," explains Sass. One cup a week can also help prevent high blood pressure, according to 2011 research.

Red wine: It's loaded with polyphenols, which help improve blood flow. Women who enjoy a glass or two of red wine a day report more sexual desire than teetotalers, according to a study done in Italy (naturally).

Watermelon: Thank citrulline, a nutrient that sets off a chain reaction to relax blood vessels and increase circulation to all parts of your body, according to research from Texas A&M University.

Chickpeas: The humble garbanzo bean is a terrific source of zinc, which has been shown to help regulate testosterone levels in men, says Sass. For a date-night appetizer, serve him a batch of roasted chickpeas or some roasted veggies with hummus.

Licorice: A study by the Smell & Taste Treatment and Research Foundation in Chicago found that the scent of Good & Plenty licorice candy, when mixed with the smell of cucumber, triggered a 13 percent increase in vaginal blood flow. Go figure!

This article originally appeared on Health.com.