Anal?

My boyfriend keeps asking me for anal and I just don’t want to do it I would if I could and not only that I have problems going to the bathroom sometimes like I would try it if I didn’t have trouble with going to the bathroom but Idk how to tell him I can’t just tell him “ I have troubles with me shitting” like I don’t know how to tell him without grossing him the hell out I’m embarrassed about it to the max but I really need help and every time we’ve tried it even with lub it hurts me so bad