I had this problem for awhile. I don't know if this will work for you, but after trying vibrators etc. and had no luck, I discovered the Coital Alignment Technique.
If you google this, there is A LOT of information on how to do it. In the tradition way, it's done with the man on top, but I highly recommend trying it with the woman on top. When you are on top of him, move your pelvis down just an inch or so lower, so your clitoris is up against the base of his penis/pubic bone. Instead of doing a thrusting motion, do more of a "grinding"/rocking back and forth motion rather slowly. It may take a few minutes for it to really build up but it makes me orgasm every time. Having him tilt his pelvis upwards may help a bit too.
I know for me this helped a lot. I was one of those woman who could only even get herself to have an orgasm through masturbating if I had a pillow between my legs and humped it. This produces a very similar effect.
I hope this helps, and good luck!