I have also developed what might be an allergy to lambic. I am allergic to all sorts of things according to the allergy tests (molds being one of them). So, I wonder if something in mixed fermentation sour beers now screws up my stomach. Its weird because there is a clear hierarchy to what does it, and it is strictly sour beers. Tilquin is by far the worst and Boon is the easiest on my stomach. Also, certain sours don't seem to cause any problems.
Really weird, especially since I was into this hobby for over 2 years until it started.