when i have sex i dnt cum and smetymes its painful

Well, how old are you? If you haven't reached like 13, you MOST LIKELY won't be able to cum. And are you male or female? I'm female, and it hurt really bad the first couple of times i masturbated. I haven't had sex, though. But if you have only had sex a few times, and you haven't masturbated much, it's probably because your "private part''  isn't used to being aroused like that. So just practice more and don't expect to cum if your not over 13 or so. :) Good Luck!