"Pretty Little Liars" quickly became one of the most talked about shows on television when it premiered in 2010.

Sasha Pieterse was only 13 when she started playing the presumably murdered, 15-year-old "queen-bee" Alison DiLaurentis. A few years later, the actress would start to notice changes in her health, particularly her metabolism.

"The changes that were happening to me were documented on camera… At 17, I gained 70 pounds in the year… for no reason… There was no explanation for it," Pieterse revealed on the podcast "The Squeeze" with actor Taylor Lautner and his wife, also named Taylor.

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Sasha Pieterse in a white calf length gown with her left hand on her hip split Sasha Pieterse in a blue long sleeve dress with a black belt and her left hand on her hip in the middle a picture of Sasha Pieterse with bright under eye makeup on the carpet

Sasha Pieterse says it was hard being on such a wildly successful TV show as "Pretty Little Liars" when she was a teenager due to health changes. (Albert L. Ortega/VALERIE MACON/David Livingston/Getty Images)

"I went to over 15 gynecologists… One gynecologist told me to my face that I was lying," the actress admitted. "That I must be eating terribly, and I must be doing everything wrong because ‘look at you,’ was essentially what he said."

"I just wanted somebody to test my blood… It was the most frustrating experience… and disheartening because no matter what I did, no matter how well I behaved, no matter how great I treated my body, things were actually getting worse rather than better. It was very, very confusing," she explained.

Sasha Pieterse in a pink dress that is belted with her left hand on her hip in 2013 split Sasha Pieterse in a black flowy gown on the Warner Bros. set in 2017

Sasha Pieterse is pictured at an event in 2013, left, and on the Warner Bros. lot in 2017. (Paul Archuleta/Jerritt Clark/Getty Images)

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Pieterse said she was eventually referred to an endocrinologist, who was able to diagnosis her with polycystic ovary syndrome (PCOS) practically right away.

PCOS is defined by the Mayo Clinic as being a "problem with hormones that happens during the reproductive years. If you have PCOS, you may not have periods very often. Or you may have periods that last many days. You may also have too much of a hormone called androgen in your body."

Another common side effect is weight gain.

Sasha Pieterse as Alison DiLaurentis in "The Perfectionists" wearing a black blazer and looking slightly distraught split Sasha as Alison in "Pretty Little Liars" season 1 looking perturbed

Pieterse's character of Alison DiLaurentis looked different throughout the series and on spin-offs. (Allyson Riggs/Jaimie Trueblood/Getty Images)

Pieterse said it was difficult growing up on television while experiencing such profound changes to her body.

"I had such a good experience, but at the same time it was very intense for those 7 years… It's really intense to learn and grow and understand yourself when everyone else is hyper-analyzing it," she shared.

Sasha Pieterse smiles in a red dress in Universal City

Pieterse revealed her PCOS is now dormant. (Paul Archuleta/Getty Images)

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Pieterse, 27, says that having her son Hendrix actually regulated her hormones, so much so that her PCOS is now dormant. She explained that childbirth can, albeit rarely, help women with the problem.