I should also say my usual bit about looking for an underlying cause. In my case it was heavy metals (mercury from my silver fillings, but there are other metals and other sources). The anti-yeast treatment can help you control the symptoms, but the problem likely won't go away if there's something else causing it. Heavy metals are probably a very common problem, so I suggest you look into the possibility first.
I've also heard of people feeling better after replacing their root canals.