Is there something different about lagers that may cause an allergy?

Ive recently realized that when I drink lager, particularly Sam Adams and Budweiser that I get a really upset stomach and get sick for a few days after (Recently realized as in I recognized it wasnt just beer, it was was those beers in particular.) I am fine with other beer, so is there something in the beer that makes it different, or is it in the way it is prepared?