How can I make my girlfriend orgasm?

I have been dating my girlfriend for over four months now and i cant make her come. i have like once but even then she said it wasnt the same as when i finger her. i can make her come really fast when i do oral but not when we are actually having sex. I have talked to her and do whatever she wants, i have tried lots of positions and we both last forever but she never finishes. What do i do?