how do you loose weight after being on steroids?

I just had brain surgery to remove a tumor. They put me on steroids for about 2 2 1/2 months. I gained about 40 lbs. I couldnt help it, but now im going back to school and i look so much different.Im only 15 years old. When your on steroids its hard to not eat.. I ate so much. But now Im back to my regualr eating habbits.. any ideas?