Allergies Support Group
When the immune system responds to a foreign substance in an abnormal way, it is classified as an allergy. When the body first contacts the substance, it will not cause any reactions, but the immune system will start to produce antibodies to it and subsequent contact will trigger more dramatic responses. Depending on the allergy, the response could be mild or very severe...
If s/he can't answer them, should refer you to an allergist. An allergist can also safely test you via blood or scratch test for food allergies, so that you can see what ingredient you have developed a sensitivity to and thus that which you should avoid.
Good luck.
Could be any number of things. Does sound so scary, though. Something must have been different about this pizza, if you've never had any bad symptoms before. Or maybe you have suddenly developed an serious allergy. I know that there are some foods that are less likely to cause allergies (i.e., rice). I am sure that you can look them up and stick to those until you get to see an allergies.