Well, lactose was an idea, with the pizza delivery. Still, there are a whole bunch of food triggers for which there is no test. Mine is sulfite, but your's is probably different.
All I can suggest is try keeping a good food journal - including everything you eat, drink, meds, along with date, time and any reactions. That's what my allergist had me do, and my list of trigger foods - things like gelatin, maple syrup, sodas, wine and beer - googled out to be sulfites. At least this test if free, easy, and no payments to doctors. You cold come up with salicylates, MSG, any number of other triggers.
It takes a couple of months, sometimes more if you need to include "challenge testing." You can find all sorts of threads on those subjects.
Meantime, maybe someone else will come along with more answers.