Let me get this straight. You had sex 6 years ago, you've been tested three times since then for HIV, all negative, but suddenly you've become paranoid because you've had some yeast infections and athletes feet?
If you were tested at least three months post exposure, the tests would have been 100% conclusive that you were, and ARE, negative.
Yeast infections can happen for a number of reasons. One of the most common is being on an antibiotc. Have you been on any? And athletes foot can be picked up in many public places like the local swimming pool or wearing someone else's shoes or it can happen if your feet sweat alot and you don't wash and dry them well.
Normally I would say you have absolutely no risk for HIV given your history as I understand it, but you say this is consuming and ruining your life. I would suggest you have a frank discussion with your doctor and see if he/she recommends another test, even if only for your peace of mind. If that doesn't calm this fear, then therapy would be the next logical step since you fear where this is taking you.
You could post your concerns over on our HIV Prevention Forum. The folks there are highly qualified to answer your questions.
I wish you the best.