I think it's because some meds make you hungrier, thus you eat more. And then it becomes a vicious cycle---you feel bad so you eat more, and then you don't feel like exercising because it's hard to move your body, so you keep eating and don't burn it off.....and round and round it goes.

Your medication profile isn't too bad. Abilify, like any atypical anti-psychotic, can contribute to weight gain but is less likely to do so than, say, Zyprexa or Seroquel. Lithium is also often implicated in weight gain, partially due to increased appetite but also water retention. Talk to your prescriber about your concerns.