Since the OP asked for suggestions, one thing to try is a combination of oral and manual stimulation. Make sure that he is focusing on your clitoris with his tongue action. Tell him what feels good. When you are well lubricated, have him slide a finger inside of you about 2" or so and make a "come hither" motion with his finger. This allows G-spot stimulation while simultaneously stimulating your clitoris. If this does not do the trick, you just may not be wired to achieve orgasm this way.