Your diet sounds pretty similar to mine. I eat lots of grass fed beef, bison, fish, pork, eggs and a decent amount of quinoa, buckwheat, brown rice pasta and sweet potatoes. I avoid nuts and the only dairy I have is a whey protein shake 4-5x a week. Again very similar to you, very strict to my diet, all organic and only ate a sandwich once in the past several months.
Which stool test did you get for candida? What I'm wondering is that even though my stool test came back negative for candida, I'm wondering if I may have a candida issue in my small intestine? I'm starting to think the Organix Acid test from Metametrix might be my next step.
I've been researching this like crazy too and its mind boggling how many different possibilities it could be. I'm also very curious about the liver since its the major detoxifier of the body. I wonder if Liver Flushing would cure the issue?
I'm also looking into intestinal putrefaction, gut fermentation as possible causes.
I asked my mom the other day if my breath smelled foul and she said she could not smell anything terrible. I know when I taste that sour/metallic taste it makes me feel like my breath must stink, but perhaps its not terrible.
Either way something is up and I need to get to the bottom of this.
And yes its very nice to discuss this, here's to hoping we both find a solution and soon!