Sometimes its really difficult. When I went through this issue myself I asked to be changed to another mood stabilizer and I found Lamictal to be the most tolerable in this regard, certainly as regards weight gain but each person responds differently to each medication. Sometimes if a person is developing severe side effects from a medication it is worthwhile to consider available options. Speak to your psychiatrist about this.
I'm seeing the same thing and am on Lithium, lamictal and Seroquel. I'm not eating any different than I was before and am actually trying to watch the calorie intake. how the heck am I gaining the weight?
All the atypical antipsychotics have the potential to cause metabolic imbalances that often lead to weight gain and can create the changes that lead to diabetes, Abilify, Fanapt and Saphris being the 3 with the least of this potential. Eating a proper diet of course can help strongly but it still can be a problem. I would not know what further changes to make but you could speak to your psychiatrist and if it becomes a severe problem they could change and/or adjust treatment and refer you to a nutrionist if neccessary.
I would say to make sure you are getting some exercise, especially if you were on a healthy diet before. My psychologist told me that sometimes when you stabalize and you're not being manic as often, sometimes you don't realize that you're not doing as much physically as before (if you were one of those get up and go mania people.) So you do not realize that not only are you on a medication that can cause weight gain, but you're also not burning as many calories as you were. So maybe just start doing some extra exercise and see if that helps.