Food Allergies Treatment

I am currently awaiting the test results to find out what all my son is allergic to since something he is eating drinking or coming in contact is causing to vomit and have diarrhea. I am thinking it is a Milk allergy. So if that is the case many food we eat contain milk or are made with milk. So now what do I do? He is four and I am afraid he might not take to lactose free milk products. Does anyone have any suggestions? Other Information he couldn’t tolerate regular or soy based formulas as an infant. He was on Simalic Alimentum.