Have you taken him to an allergist (a real specialist in allergies, not just a pediatrician), or an opthamologist? It's imperative that you don't take him to an optometrist, who specializes in vision correction, but to an opthamologist, who specializes in eye diseases.
If you take him to an allergist, there are three levels of testing. One is a quick blood test, which tests for about 26 common food allergies. One is skin prick testing which tests for environmentals (trees, grasses, pets, dust mites, flowers, weeds, etc). The third tests for earth compounds (metals, things that naturally occur in soils and rocks, additives in medications and cleansers and shampoos and soaps and sanitizers, antibiotics and antibacterials and antifungals and perservatives, fragrances, etc). It's called patch testing.
If your son's doctor is saying he may have allergies, it's important to get to the bottom of this.
And while you're waiting for an appointment with an opthamologist or allergist, keep a detailed food journal and a detailed log of his activities (does he walk through a park to get to school, does he play baseball on a particular field, do you have pets, etc).