I had the same thoughts before I had my first anal orgasm and it was actually my top who told me to embrace it and let it happen… it does feel like you have to go right before and sometimes as a bottom that feeling can be unnerving but if you are confident in your hygiene go with it and ride that wave... IT IS GREAT!!!!
as far as it hurting might just be you tensing because you are scared... if rimming relaxes you make it mandatory for your partner. make it one of the things you discuss before he/you even get there. but it should only hurt briefly in the beginning at most... but if you dont relax you are only hurting yourself and most likely its in your mind
I rarely get erections while bottoming and Ive honestly only had a few tops ask if i was enjoying the sex but just tell them that your focus is on your ass and thats is where your pleasure comes from while bottoming and they are usually ok with that but I on the other hand cream a lot, moan and have multiple anal orgasms so thats evidence I am enjoying myself.
yes it could be the fault of the top but I found that when I told them i was tense before hand they are more caring and try to relax me so it doesnt hurt as much... some have massaged me, some have kissed me, some have taken it slowly and made it hurt a lot less.. communication is key