They need to remove his tonsils. More and more doctors are becoming reluctant to do tonsilectomies because they are starting to believe the tonsils serve a higher function than previously thought, they are a part of the immune system, but with that many instances you really might want to request they be removed.
My doctor drug his feet and did not remove mine until about 8 years ago when I was 17, said I would have to get a lot sicker than 8 or 10 times a year. I can tell you right now I would have missed a fraction of the school days I missed had they taken them out earlier. I was in the doctors office every 2 or 3 weeks sick again by the time they agreed to the surgery, but we let it go on too long, we could have prevented a lot of pain on my part having done it sooner.
Now I rarely get sick! One cold a year maybe, the very occasional severe illness every few years, but the surgery was well worth it and compared to how ill I had been, relatively painless. I had bouts of strep that hurt ten times worse than how my throat felt after the surgery. Do it while he is little and save him the trouble he'll have later.