Orgasm trouble

I think I have a problem. I can only orgasm on my stomach. I started masturbating 2 years ago, and have only done it on my stomach ever since. I have tried several times to orgasm in different positions, but I have to flip on my stomach to actually orgasm. My boyfriend is amazing at making me feel good, and I get close to orgasm but I just have to fake it because I dont know how to tell him that I have to flip over. I want to be able to orgasm when he eats me out and when we eventually have actual sex, but I dont know how to stop this. Is it a mental block? I have no idea but it's so frustrating to fake orgasms when I'm really so close to that point. I just want to be able to orgasm in any position.