I don't enjoy sex?

I'm 18 years old and my boyfriend and I started having sex a few months ago. I can feel it just fine but it isn't pleasant. It doesn't hurt or anything but even clit stimulation hasn't helped anything.
I have amazing orgasms when I masturbate so I know there isn't anything wrong. And I'm very comfortable and open with my boyfriend so I don't understand why it's so bad. It's gotten to the point where I don't wanna have sex anymore.
Any advice?