Demi Lovato has been opening up to the press about her struggles, and now the 18-year-old star tells People that she is not only battling anorexia and bulimia, but bipolar disorder, too.

"I never found out until I went into treatment that I was bipolar," she reveals. "Looking back it makes sense. There were times when I was so manic, I was writing seven songs in one night and I'd be up until 5:30 in the morning."

Lovato filmed a candid interview with 'Good Morning America' and '20/20' in which she reveals even more details about her recent struggles. "I was bullied for being fat," she says about the impetus of her eating disorder. The full interview will air on ABC on April 22.

In November 2010, Lovato dropped off the Jonas Brothers' tour and checked herself into a rehabilitation center. After completing three months of treatment, the Disney star posted a video message to her fans crediting them with giving her the support that got her through her tough times.

On Tuesday, Lovato announced that she will not be returning to 'Sonny With a Chance.' Instead she will be focusing her efforts on her music.