I want to masturbait but my body doesn't?

Basically it's like, I'M horny, but my body isn't? Like I find my boyfriend super attractive and I think about him and doing things with him and it turns me on, but my body just isn't agreeing with me. 
Sometimes I feel really bad about it and frustrated because I want to let these feelings out, but it's hard to if my body is like "oh no baby what is you doing?"
What's wrong with me? Is it normal?
****Update 1 : **** It's like, you ever feel horny and turned on and you really want to ride your fingers and get all wet? Well whenever I start to touch myself that feeling goes away like my body doesn't want it. I don't get wet, I don't stay turned on and my body doesn't agree with me?