Seroquel is notorious for weight gain, as are many meds. They are thought to slow the metabolism. There is a book called the Anti-Depressant Survival Guide that recommends a certain diet for those on these meds. It's not the best diet I've ever seen, but it might give you some ideas.
Yes,
most antipsychotics are related to weight gain. Calories restriction is one good way to counter the effect or add an appetite suppressant. Exercise is also an important factor. You must already know that.
M4