Allergy frustration

Noah broke out into a rash again today. It has to be something that I am eating. But what?! I have no idea, and it is driving me crazy! The most likely candidate is milk, but I have been eating milk-containing products the entire time Noah has been alive. Also, strawberries, egg-products, soy-products. The entire time! But only the last 3 weeks has he been breaking out randomly. How am I supposed to figure it out...it could be anything over a 2-3 day period. Plus, he gets milk pumped from previous days, so it is hard for me to remember what I ate. I would gladly give up anything so he wouldn't have this rash, but I don't know what the problem is. So frustrated with myself!