Anal sex questions

Sooo... I've recently tried anal sex and loved it. I can't seem to get enough! My boyfriend loves it too. I get horny and seem to want it often. So far I've had it twice this week! I'm afraid that it's bad for me though...I pass gas afterward, and then feel like when you're constipated. He is a pretty good size and I'm afraid my butt hole will get big. Does anyone here do it often and can alleviate my concerns?