can't orgasm during sex... help!

Okay so my boyfriend and I have been having sex quite often for the last two weeks or so. He's able to orgasm every time but I never can.. I can't when we have sex, when he fingers me, or anything. I could always orgasm when I masterbated but I don't know why I can't with him... I feel like he's getting discouraged and I hate it just as much as he does. Any tips or tricks we can try??