Orgasm...

Help! I've been with my boyfriend for 2 years now, and the sex has always been amazing, especially when he goes down on me. But recently I changed my contraception and now I can't even get close to an orgasm when he goes down on me. It annoys the both on us because I'm laying there waiting for it and he's getting annoyed because it's taking ages. We've tried different techniques to try and stimulate me but it never seems to work. I'm always aroused and in the mood but I can never get what I'm waiting for. What would you suggest?