The Fashion Star judge gained a total of 80lbs prior to the birth of her first child Maxwell earlier this year.
Simpson signed a spokesperson deal with Weight Watchers for $4m (£2.46m) to lose the weight, and has since shed 40lbs.
However, some critics have slammed the singer and reality show star for failing to lose the weight sooner.
Sources tell BreakingNews.ie that Simpson is now distraught over the harsh comments about her weight loss.
"For years, Jessica has been okay with her body and everyone loved her for that," a source explained. "But now she's not feeling the love and she doesn't like it.
"She's trying to conceal her hurt feelings with humour right now. She uses jokes and goofiness to hide the fact that she's really sensitive."
Simpson recently revealed in an interview that she was shocked to learn her weight gain wouldn't come off with the baby.