Have you tried nipple stimulation at the same time? My nipples are very sensitive, but it depends on my mood if I want to play with them while masturbating. And I assume it differs from woman to woman for usefulness.
I don't know how you generally masturbate, but have you tried just focusing on one area? Even spots that aren't supposed to be overly sensitive, like the bottom of your vagina. It's a bit awkward, and I can't be sure I'm not hitting other places at the same time, but I've played with just the bottom of my vagina, and it feels interesting. It's I guess, self-foreplay.
I find it interesting to just stimulate one area, rather than everything. And then, when you are ready, do whatever you have to do to get off.
And have you tried your g-spot?
One other idea... I've discovered that lying face down gives me different sensations, for some reason, than lying on my back. So, try lying in different positions... and even on the toilet.
Definitely stay relaxed. Good luck!