My son is 5. He is hyper, easily distracted, defiant, and has great difficulty sleeping. He was kicked out of Montessori school after being put in time out daily until he became aggressive and kicked in the teacher's door. As a baby, he had colic, never slept deeply, had a red ring around his anus, green foamy stools sometimes, gained a lot of weight for the first 3 months and then dropped off, and sometimes had a bit of rash on his scalp or rosy cheeks.
At some point we convinced his pediatrician to do an allergy test on him. She took blood and tested for maybe 5 things. I never got the report, but she told us he doesn't have any food allergies. I've mentioned food allergies again, but she looks at me like I'm crazy. I think if I could ask for something more specific, like a particular kind of allergy testing or list of items... she would probably go along with it.
Our kids are on medicaid (peachcare) so we'd prefer something that would be covered. I don't know how often insurance covers this sort of thing. We aren't really in a position to pay a lot out of pocket.