My 7 year old son has had recurring high fevers every 3 to 5 weeks that last from 2 to 4 days. (This past fever is the 5th one that has occurred). He has been diagnosed and treated for strep and sinus infections, but nothing more. The doctors have tested for mono, pneumonia, lyme disease - all which were negative. What could possibly be wrong? He has no other symptoms aside from the high fever. Any ideas would be appreciated.