Hi - I had all my allergies tested by a doctor and nothing came back positive. I did the pinprick test and even had my blood tested - still NOTHING. But I was obviously having really bad reactions to some foods and pollen. By bad reactions I mean severe migraines and nausea lasting for two days.
Eventually I was diagnosed with hypothyroidism so these food intolerances are definitely a symptom.
The only way I figured it all out was to do a total exclusion diet and gradually re-introduce things. I am still working on this - I now know for sure that I am intolerant of alcohol especially wine & gluten. I gave up gluten about five months ago and I accidentally had some on two occasions. Both times I was violently ill with a migraine and nausea. Previous to giving it up I used to have the occasional gluten product without obvious problems. It was only when I had a lot that I had the bad reaction. But since stopping I can't have any at all without a bad reaction.
I have heard of other types of allergy/intolerance testing but that is the only one that I know works for sure. Of course it's a huge pain!
You could test for gluten, dairy, corn and nightshades (tomatoes, peppers, etc.) for a start as these seem to be the most common.