Ladies I need some helping reaching the Big "O"

So I have been with this guy for 6 months and we are crazy for each other when it comes to sex which is pretty great BUT I only really get the big O when he's eating me out which is fantastic because I get it multiple times and occasionally I will also orgasm when I'm on top and it's only a certain position and angle that works. When he's on top of me or we are doing doggy style there is no chance for me getting off. Do you guys have any tips because that would be amazing!