Why can't I orgasm during sex?

Hello everyone I have a small dillemma. Me and my girlfriend had sex for the first time like 4 days ago and again today. I thought my first time it wasn't so abnormal that I couldn't *** but it happened again (no orgasms for anything she does). For some reason I don't leave with blue balls, I love this girl and am very happy with her, but that being said I'd love to know if I could fix this problem, and she's willing to help. We have lots of foreplay so I don't think that's the problem. I'm uncut and pretty big (no need to lie I'm not trying to impress anyone honestly) but maybe that info helps (especially the uncut thing?). We are very comfortable with each other and I am apparantly doing a great job as I have made her orgasm several times. She is very tight and all of the sex that we've had, I've honestly not felt anything that would be defined as amazing. It hurts sometimes trying to put it in and sometimes she's so tight I can't even fit my whole thing in. I haven't really come close to orgasming either. If anyone has any advice that would be much appreciated and I hope I'm not shooting in the dark here, thanks in advance!