Help.

My boyfriend and I have been having sex for about 6 months, and I've never orgasmed. It's always...nice I guess. I mean it's ok, but, I'm starting to feel deprived. I'm beginning to resent sex and I feel like it's starting to affect our relationship...it's like no matter what he does, it never happens. It's started to build once or twice but then it's gone. Please help.