Has he been tested for any allergies? What foods have you restricted? When I was a child, I had frequent ear infections and finally had my tonsils removed. Turns out, I'm allergic to tobacco smoke! Of course both my parents smoked. My daughter developed a couple of ear infections while visiting her grandparents. Her grandmother smoked. Maybe there's something in your child's environment or diet that has been causing problems.
Also, vitamin c and bromelin are really good natural anti-histamines.