What you wrote points very strongly towards mercury. But I don't know why you wouldn't be feeling a reaction when you are chelating. You certainly should feel something. Some people feel OK during a round of chelation and then feel bad between rounds. It sounds like you aren't feeling anything during or between rounds.
I think you are right to keep trying chelation. Perhaps it will help you even though you aren't having the usual reaction people have. There is a fair amount of variability in the way people react, so it's hard to say that it's definitely not working for you.