My 17yr. old son has had a throat problem for 5weeks. His tonsils are swollen with patches of what looks like infection. He has had two swabs done that come back negative for strep. A mononucleosis test, negative. A white cell count and liver function, all normal. He has had amoxicillin , cecor, and is now on clyndamicin. It starts to improve and then flares up again. Any suggestions?