I would second Oakleaf's suggestion. Son #1 had constant, I mean constant ear infections, starting at 18 months until age 3-4. At age 2 he was on a a 1X a day dose of Amoxycillin to control them. That did break the cycle, though.
Then came the constant ur infections, and strep throats. Had an allergy eval at age 4 and started on 4 shots a week. Found out he was allergic to a lot of the grasses in AZ, where we lived. The kid could not go out on the playground at one point, it was so bad. Finally, the throat business got so bad that right before we moved to MA, he had the tonsils and adenoids out at age 7. Bingo... all of it went away. He never resumed the shots when we moved here and was fairly healthy after that. We did find out he is lacking an immunological protein at the allergy eval., so if he does get sick, he knows now as an adult not to let it ride too long. But basically, the allergy eval. plus the tonsillectomy did the trick.