First time anal...

Today my boyfriend and I tried anal for the first time because he has wanted to and I finally felt comfortable enough for it. I'm still in pain and... TMI... Whenever I go to the bathroom (even if it's just to pee) I end up farting and a little comes out that is very runny! Is this because of the lube and/or because he finished and wasn't wearing a condom? Am I in pain because we somehow didn't use enough lube, or would I feel this way no matter what? I didn't love the experience overall, but it made him happy so I want to do it again sometime... Is it always going to hurt this much and be this uncomfortable afterward?