You can take a simple urine test to check for pyroluria to rule it out. No sense in guessing.. http://www.kryptopyrrole.com/
If the test comes back positive, there is a lot of good info here (just go to archives and type in pyroluria).... http://www.orthomolecular.org/
Also, watch your intake of selenium. Over 200 mcg daily can give you problems and at levels of about 1,000 mcg -- or 1 milligram -- a day you may start losing hair, fingernails and have more GI distress.You already are getting 125mcg daily in your Humet and another 100mcg in your selenium supplement. Check if you have more in your daily multi or other supplements.
You are also getting 3.0 mg of Manganese in your Humet. Once you stop your iron supplementation which decreases your intestinal absorption of manganese your levels should stabilize with the Humet if you are low (unless you have a genetic issue which affects absorption/assimilation).
Check into NAC as well. I think you may benefit....