I have to take both lithium and Olanzapine how do I stop the weight gain

So I need both a mood stabiliser and antipsychotic, I’ve tried most antipsychotics and only really respiridone (had to stop due to high prolactin) and Olanzapine work for me, I have a dog so I exercise everyday, eat smaller portions, less junk but I’m still gaining weight is there a way to to minimise the weight gain?