Take him to a naturopathic doctor and have him tested for food allergies and food intolerances. He has all the classic signs of someone who has issues with food(s) and how they affect his body.
I am allergic to milk; when I was a teenager, I drank gallons of milk everyday and didn't know it was because my body craved something it shouldn't have. I am also gluten intolerant, and until I found out, I would stuff artisan breads into my mouth faster than someone could spit, because I craved it SO BAD.
You can call the pediatrician or aother allopathic doctor, but I really, really think you'll get more results and have a doctor who will work more with you to resolve this issue if you take him to an alternative healthcare doctor, as they work with food issues everyday; allopathic doctors don't deal with nutrition and you might take years and years to find out what's wrong with your son.
Believe me, I've been there, both for myself and my daughter. My daughter has Sensory Processing Disorder, and when we discovered she also had food issues, taking away the offending foods and eating a better diet made drastic improvements in her.