I had a girlfriend once who had almost the same reaction as you. She would experience a sensation of "done" exactly as you described, but no big bang, even after very very intense play.

After 9 months of play, I decided to give up. Not on her --she was a great gal, and we remain friends to this day, but rather on her having the big "ohhhHHH" moment. Essentially, she wasn't willing to experiment. She had been raised to think that all sex was evil, and touching yourself even moreso.

But that doesn't seem to be the case here, tho. However, my hunch is that you are not quite finding the right spot for you. I wish there was a way to give you the winning cupcake recipe for orgasms, (Take one pair of bagels, add a 12oz bottle of mayo and one pair of tweezer nipple clamps,) but there isn't. Most likely, after 13+ years of masturbation without intent to orgasm, your hands/body/pussy are trained to go to a preset location. After all, it's comfortable!

I would try changing the routine around. Use a different hand for a bit. change the circumstances of your masturbation. Try standing up, or laying down, or lying out in a hammock swaying in the breeze. Try leaving your pants ON, or off, as the case may be. Try more lube or less. Use a Hitachi Magic Wand and close your eyes, letting your sensations glide you. If you already use the good Dr. Hitachi, then switch your speeds. Try using a small amount of penetration. You don't have to stretch yourself like a fisting queen, but some women NEED those hormones released during penetration in order to set the stage for a rolicking orgasm.

You are already familiar with your body and your clitoris, so you are already ahead of the game!

Lastly, you didn't mention whether or not you have a lover. If you do, and you can cum with THEM, ask them to show you what they are doing down south. I have never had a partner say "no" to mutual masturbation -- the best safe sex there is!

Happy exploring!