It's dangerous to do food challenges at home when you have bad reactions. I also know it's expensive to do it in a doctor's office, but you should consult an allergist about
Do some reading on the many sulfite posts in this forum. Just put sulfite and any other key words you are interested in in the "custom search" box at the top of the page. I don't know if it's possible for mold to cause sensitivity to sulfite or anything else.
Don't buy any fast food, processed food, or food on sulfite lists that contains high amounts of sulfite. It's not possible to avoid all sulfite. Keep a journal for both you and your son. Plain water should not contain sulfite unless it's well water, but you can find a local laboratory and have it tested. Municipalities also have water tested and you can ask where their test results are available.
Search for "food journal" or "food diary." If you are sure you have a sulfite intolerance you can calculate the amount you tolerate from the formula in http://www.learningtarget.com/nosulfites/