I would be highly skeptical of tests the doctors give for a problem like this (that includes yeast tests and heavy metals tests).
A home test you could do is try an anti-yeast diet for at least 4-5 days and try a yeast killer. If you feel worse during that time, that's a strong indicator that yeast is your problem.
I followed the diet strictly and used a yeast killer 3 times a day, and I felt better in about 5 days. I felt better, but it didn't really take care of my problem. Chelating mercury from my system helped me (mostly) recover.