How can I tell my bf I don't like a certain position?

Ally • I'm 24 madly in love and I'm a waitress/hostess/kitchen help at a local restaurant
My boyfriend loves when he has me lay on my stomach and he's on top during sex how can I tell him that I don't like that position cuz I don't feel like I can get off that way any other way I can finish and be happy but when it's that particular position I get nothing. What should I do?