First off, having anal sex should not have caused this. I say should, but it appears it did. If it did cause it, then something wasn't right. Something you or he did wasn't right and if you try it again, you need to change the way you do it. Check the Internet for ways to have safe anal sex. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
I agree with the others, go see a doctor and tell him or her exactly what happened. Believe me, they've already heard it, and probably did it.
But I really wanted to comment on some of the first comments to your question. I'm guessing they were from women because they all pretty much said "why would you want to do that????". Anal isn't for everyone. But anal is what it is (for me) because of it's forbidden, because it's naughty, and because it's so off limits. I know some people are into scat. Not me. In fact, I want to avoid that if at all possible. And us guys are fully aware we are messing around the source of scat. And yet most of us don't want it. It's hard to explain. A women’s butt is her most private area, the area she keeps secrete, the area she is most embarrassed about. Guys are too. But because it's off limits is the reason I'm most interested in it. Not that I'm trying to embarrass her. And when we do something “back there” and see or smell something, it just makes it real.
I was born and raised Catholic and I still think (somewhere very deep) that I’m getting away with something. Some girl (women) is letting me stick something up her butt. That’s dirty (as in naughty) as hell!
So ladies, don’t judge this person for trying anal sex.