My husband and I tried anal sex for the first time. I didn't have a problem with it because I've done it before in a previous relationship, several years ago. But when we tried it, it burned and was painful. Which was strange because my husband has a average sized penis, and it didn't hurt going in but once he got more than the head in it started to burn when he started moving it in/out. What could be causing this burning? Could weight gain cause it? I really need help with this!