anal sex

My boyfriend always bugs me about having anal sex. I have with him before and he absolutely loved it and so did I, after I got past the painful part. It's been a little over a year since we've done that at all and now he wants me to but I just can't get past the pain this time. I don't know what I did to get through it before. Anyone ever have anal sex and know any way to get past the pain of first doing it?