P.B.
Wow, how frustrating and heart-wrenching for you! My first question would be do you have insurance? Most insurance companies have coverage for second opinions- I would recommend that you tell the specialist here that although you value his expertise, you want to see another DR. for a second opinion. They should be either (1)giving you a diagnosis of what is wrong with him, (2)testing further right now to find a diagnosis, or (3)telling you that as far as they can tell nothing is wrong with him. Not stringing you all along and having you bring him in to the Dr. or ER anytime he has a cold symptom. Has he been tested for allergies or anything?
Sometimes at hospitals they have a person called a "Patient Advocate" who works with you and your/your childs doctors to basically be your voice to the doctors- to demand information and proper treatment. You could check at the hospital OR perhaps with your family doctor to ask about that. OR there is a non-profit organization called "Patient Advocate Foundation" that you can contact at (800) 532-5274, they also have a website but I don't remember the web address off hand.