Your reaction to the DMPS seems to me like a reaction to the mercury (or other heavy metals) being circulated in your organism.
Maybe your doctor didn't emphasize to you that chelation is not enough - all the heavy metals being circulated MUST be excreted - through feces, urine, sweat.
Otherwise they probably will deposit elsewhere in your body causing new problems - hence your weird reaction.
After the IV chelation every week, I have to do a colonic or at least a coffee enema to flush out all the heavy metals.
But done properly, heavy metal chelation is TOTALLY worth it - all metabolic process in the body start working better and your energy levels go way up. Also, I noticed my immunity is much better now, functioning almost normally whereas before I could drag a cold around for MONTHS. The improvements are subtle, but they are there.
My advice to you would be to find an excellent environmental medicine specialist. I go to the Southwest College for Naturopathic Medicine, here in Scottsdale, Az - and I garantee you, doctors there are great and I am being very well supervised.