Anyone know the best way to test for a food allergy?

I believe I have one associated with a spice in Southwest/Mexican cooking

The last few times I have eating Mexican food, I started having 2-3 days of intestinal pain. Last year, I ate at some place in Key West that eventually led to vomiting and it didn’t really clear up for 3-4 days. I thought it was food poisoning, but it looks like an allergic reaction.

It happened similarly (but not as severe) from La Carretta on Tuesday.

It started few years ago. Then, I would break out in a rash similar to niacin flushing in the face, ears, elbows, etc but it would pass in less than an hour.

TIA