Chiropractor. When the neck is out the sinuses do not drain properly and get clogged. If you are not comfortable with manual manipulation you can easily find someone who uses an activator, a tool that was developed for astronauts. Very effective. Chiropractic care can boost his immune system and there is no such thing as too young to see a chiropractor.
You might look into a salt pipe for him. Salt air is incredibly healing for respiratory ailments. Here's a link that gives you some info
http://www.portablesaltcave.com/faq.html
Local bee pollen is great at combating allergies. Pound it down for a month. I would suggest in smoothies. Superfood will build up his immune system.
Stop giving him dairy. It just causes mucus. We don't absorb the calcium. Better sources for calcium in leafy green vegetables. He may be allergic to wheat and/or corn. Yoga would be great. Yoga emphasizes breathing and is great for overall health.
Pharmaceuticals like Nasonex are horrible. I learned to treat my asthma successfully with foods, supplements, chiropractic adjustments, acupunture after being started on inhalers as a young adult. They make you feel terrible and do mess with your moods. They also take a toll on the body. There is another way. You might consider consulting an naturopath or homeopath. Ask around and get recommendations if you don't know where to go. I can recommend some people for you if you are interested.
Good luck!