sex is painful if the girl hasn't had sex in a while, or if she is a virgin, because she will have tightened up. it's actually a horrible feeling, as if you are being stretched too far.
sex can also be painful, or at least uncomfortable, if the penis bashes against her cervix too hard. i find this sensation awful.
really, for me, getting an orgasm from sex is beyond my wildest dreams. my target for now is to enjoy sex, because although i want to, my body won't allow me. it is physically painful.