If your mercury has been removed, you may want to try treatment for chronic yeast..which can cause funny symptoms. Chronic yeast is usually found in anyone who has had or does have metal. Grapefruit Seed extract and probiotics are wonderful for killing the yeast overgrowth. But you may experience a die off in the first few days, which might be gas, bloating, loose stools. Algin may help absorb the yeast and reduct the symptoms. Others use charcoal for this too.
Garlic is very high in sulfer. Some poeple are sensitive to anything high is sulfer..for whatever reason. As for the DMSA reaction, that may be the dosing. Make sure you are on proper vitamin and mineral supplements when using DMSA and that you are dosing a low dose (1/8 mg per pound) and giving it every four hours. It wears off after four hours, so giving it far apart will cause redistribution and side effects.