Wait, I'm allergic to sulfa too. What food has sulfa in it?
God, so many. So much. Too many to list, I'm sorry, and it's not just the big well-known meds (penicillin, pediazole, bactrin) but things that are "sulfites" or "sulfanomides" can set off a sulfa allergy too. It sucks but the best way to stay safe is to look up individual ingredients you're not sure about, like the actual chemical compound, and check if they fall under those.
In my most recent Bad flare, it was an artificial sweetener called "acesulfame potassium". Sweeteners like that and preservatives (which can be used in just about anything!) are Real bad. Unfortunately, a lot of labels will call them any number of names or just not list them bc sometimes they're not considered allergens, and lol. lmao.
so yeah.. it's basically a crapshoot. Same with soy variations, there are tons under different names, so. Trial and error. Sigh.