I think you should look at getting him tested (again?) for his allergies. What exactly is he allergic to? Find out, avoid the allergens, and ask the doc about allergy shots (probably too young though) or allergy meds.
The pneumonia, tonsilitis, ear infections, bronchitis, could ALL be caused by the allergy. Wet ears, lungs, sinus', increase the risk of infection.
My approach, as usual, find the causitive factor and remove it if possible, if not then treat the symptoms to avoid complications.
BTW, my kids have allergies, RAD/asthma, sinus allergies, rashes too. I try hard to keep them "dry" via use of anti allergy meds, which I have noticed fewer infections in thier ears and airways.
I understand your frustration. It's so hard to watch them suffer. So many children have these allergies. More than ever before. I've thought long and hard as well as researched for info. I can only sumise that it is environmental. Our air quality where I live is 83%, our food ? I don't even like to think of pesticides, ab, weird chemicals, etc that are used to produce our food supply.
One problem I have found is that only male plants are patented. In turn, when you buy a plant or tree from a store, it's usually male. Cities, counties, and other municipalities, as well as many homeowners, avoid or cut down the female plants b/c they are messy. They flower, fruit, and leave a mess to clean up. So all these male plants putting off pollen and no females to take up the pollen, it stays in the air for us to breath. There are now a couple of cities in America that have outlawed the planting of male trees. One is in N.M.
I'm checking out or IN as many would say, leaving the city behind, to grow my OWN vegetables, raise or hunt my own meat, milk from MY cow and goats, eggs from my chickens, and best of all, I'll have an unlimited water supply of the very best around. Same water that I now buy in the store in a bottle and pay too much for. There are plenty of natural forests all around. The air quality where I am moving is 98%. I have yet to see an asthma attack at our new place. They run through hay fields, play outside all day having fun, and I don't have to give Albuterol. I can't wait to get out of the city! I'm outa here!