Can't orgasm

My boyfriend and I have been having sex for about 3 months now, but I have yet to have an orgasm. He's my first but he's more experienced than me. Last night he asked me if I ever get off when we had sex and I didn't know what to say. I didn't want to lie, but I didn't want him to get discouraged so I said "yeah sometimes." I don't know what's wrong with me :(