Hi, I'm so sorry to hear you're experiencing such a troublesome issue :( I'm glad to hear you've had some recent success in working out what the issue is.
My very first thought when reading about your experience was that perhaps you're not using lubricant, or not a suitable one. Since you've seen doctors about the issue this very possibly was ruled out, but it's always best to check the obvious things first. Do you use liberal amounts of lubricant? If so, what kind? Have you tried various types, and have you particularly looked into something like Sliquid, that is free of nasty chemical ingredients that may give reactions? Do you use condoms? If so, have you tried changing types and brands? Tried changing any birth control medicine you might be using? I've had a few friends who have experienced the 'intense burning pain' issue and every time it has been either lack of lubricant, reactions to lubricant or reactions to the condom used (spermicidal types always being the worst of the bunch). I imagine the doctors have covered these issues but like I said, it's always good to double-check :)
Have you thought about using some kind of stimulating balm or gel on your clitoris? I've never used these myself, but I wonder if something like Flower Power Body Balm Orgasm Enhancer (http://www.lovehoney.co.uk/product.cfm?p=506) might stimulate your clitoris enough to satisfy the stimulation requirement.
You might want to look into something like a strap-on vibrator (http://www.lovehoney.co.uk/product.cfm?p=20443 - though I can't vouch for this one as I've never tried it, but this is the concept). I have a Layaspot which was advertised as intercourse-friendly, but my partner and I are both very skinny so it tends to mash against our pelvic bones during use, someone with a little more meat or muscle might have better luck. Do look into the 'toys for couples' section for other intercourse-friendly sex toys. I think your issue is important enough that's it's worth investing the money in experimenting what works best for you (and trying new toys is always fun!).
I do hope you're able to work this out soon :) Good luck!