V.T.
When my daughter had a milk-protein allergy as an infant, the doctor told me that if they don't outgrow it by 5, than it most likely is a long-term allergy. It may not be an allergy, but an intolorance. I would have him tested just to confirm so you know what you are dealing with. My nephews are allergic to peanuts. Even at 3 they would tell you that peanuts make them sick. They didn't have anymore details than that. If it is an allergy just start telling him now so he knows and can have some control of it. Especially if he goes to school and starts food sharing with other kids. The adults may know, but they may not always see the kids sharing.