I can't orgasm with my boyfriend of 2 years.

So my boyfriend of 2 years and I started having sex in January. We were each other's first. He feels great and all. But... I can't orgasm. I think I only have 3 times, never from penetration. I feel bad because he gets discouraged. I feel like it's my fault and that I'm making it harder for me to orgasm. I don't know what to do. I love having sex, but now I keep thinking that he's not enjoying it. Or he feels obligated to try and make me cum. I'm so frustrated.