everybody's body reacts differently to meds. Some may gain weight with increase on appetite, or some will lose weight with decrease on appetite. I am on seroquel and abilify, and so far they havent caused any weight gain for me, or weight loss! I was on geodon at one point to, but that was a nightmare! You will have to sit back, and see what happens. If you really dont want the weight gain, then exercising should definitely help! I cant say for sure either, what the result will be!
I don't know on those particular meds, but I was on some antipsychotics for a while and still managed to lose weight, so there is hope!