You tested negative, and the tests are very reliable. You can trust that you don't have herpes.
What do you have? Well, obviously, I can't say for sure, but perhaps it's anxiety and stress from all of this, or an allergic reaction to something. Try changing soaps or body washes or whatever you use. If you use something scented, try unscented. Even if you haven't changed products, maybe your product changed formulas.
Try unscented laundry detergent, and make sure your underwear is 100% cotton. If possible, try all white underwear. You may be reacting to a dye in your underwear.
Just keep trying and working with your doctors until you find what's causing it.
What about the possibility it is a different STD? Maybe your partner did not only have HSV2. Just a thought. I'm no expert at all.