I'm sorry to hear about the MCS. That's tough. I used to have sensitivities to various odors--resulted in an asthma-like experience. I'm still somewhat sensitive to more than a little caffeine and phenols.
People in the heavy metal groups who have MCS (often Arsenic + mercury) usually have to start with very low doses of supplements and gradually work up to useful levels.
they sometimes have to try different forms--Mg glycinate rather than oxide, etc.
Sometimes it is better to take the supplement with food, esp with oily supplements--Vit D, E, etc.
Think about what happened around the time your health changed. At some point if the issues are not resolved, you could consider the involvement of heavy metals. Dr A. Cutler and Dr D. Pompa describe their challenges in getting their mysterious symptoms diagnosed. http://www.healthcentersofthefuture.com/DrCutler/
I don't know what percentage of cases of AF involve heavy metals to some extent. However if HMs are involved you can bet that there are a list of symptoms and the doctor is wondering if you are a hypochondriac. The symptom lists in this library of hair tests provide good examples. http://livingnetwork.co.za/chelationnetwork/hairtest/hairtest3/