Help to get an orgasm!

I seriously need help. My guy is super great at giving it to me but when it comes to me cumming I have a terribly hard time. It feels GREAT and my guy has a reasonably fair size member and he tries his hardest to get me to finish. I want to orgasm 4/5 times we have sex without making him feel uncomfortable or to have to put him in an uncomfortable position just so I can come. Please help!