How do you relax, stop thinking, and enjoy sex?

I feel embarassed to show myself experiencing true, genuine sexual pleasure to another person. I try to make it enjoyable for him so I'll moan and eventually fake an orgasm (I know, it's bad!) but I can't get out of my head and stop freezing up when there's the potential for something to actually feel good for me. I feel like I'll never be able to actually feel pleasure from any sexual act and I'll never be comfortable enough to just let go.