Broken?

I've been with my boyfriend for about a year now. Before I met him I had only ever had sex once. I honestly don't even count it as sex. Anyways I would say we have a pretty great and healthy sex life but for some reason we can't seem to make me cum. I've tried on my own and we've tried together numerous times. Am I like broken? I thought at 20 I would know my lady bits well enough to do this stuff by now.