"Frankie is totally devastated by how she feels people are picking on her," a source close to the Saturdays singer, who is thought to be four months pregnant with her first child with fiancé Wayne Bridge, told new! Magazine.
"She's already extremely emotional and hormonal. To feel that she is being judged all the time when she is just trying to do what's right for the baby is heartbreaking.
"She has been trying to put on a brave face in public, but behind the scenes she's been suffering very tearful and emotional breakdowns. She just bursts into tears when she sees these nasty comments."
Frankie, 23, recently admitted she is having a hard time adjusting to her changing shape. "I'm having to get used to my body changing," she said.
"If I wasn't on stage and being photographed all the time, I think I'd be more relaxed. There are a lot of things to get used to.
"You can look good from one angle and not another. I think black is definitely the way forward with my pregnancy."
Last month, the petite star took to her Twitter to break the happy pregnancy news. "Some big news from me today! Wayne and I are having a baby ," she tweeted.
"We are both SO happy and can't wait for his or her arrival!"