You have to do some cardio exercises, I exercise every day at 30-60 minutes doing kickboxing, boot camp, weight lifting. If you can't get to the gym order some dvds on Amazon and do them at home. You also have to reduce your calories but make sure you are getting all you nutrients. I am hungry a lot of the time to be honest.
But I am in shape and feel good, and take psych meds.
So yes, it can be done, but it takes a greater commitment on your part than it takes for a person without psych meds.
A good website(free) is Spark People.com. You put in what you eat, and it tells you how much fiber, protein, etc that you eat, and gives you a daily summary of your intake, and how many calories you ate.
Good luck.