Suggest Treatment For Recurrent Fever And Stiff Neck

My 18 year old son has been getting fevers since September. this is his 6th fever. they last anywhere between 2-5 days. 3 throat swabs have all come back clear. he had blood work done at Christmas and they said he had strep. he has completed his penicillin ( 80 pills ) and is now experiencing his 6th fever. fever, extreme chills, profuse sweating, stiff neck, headache, and extremely tired. What do you think