A lot of people have mentioned this already, and I see that you're aware, but try to take another look at Lyme disease as a possible candidate. There's a huge controversy over it that I'm sure you're aware of.

If you haven't seen the movie "Under Our Skin", go see it now. It's all about the insanity surrounding Lyme disease, and basically the conclusion is that you need to find yourself a real expert on Lyme disease, and unfortunately they're not easy to find.