My 35 year old son has a 102.2 degree fever, complains of a lower backache , nausea , pain in his knees and weakness in his legs. He just went to a clinic and was tested for flu and strep and has neither. Clinic doc did not test his urine or blood but swabbed his throat and listened to his chest. Said he thought he heard something . Told my son to get some Sudafed and Tylenol and sent him home. Said it might be a viral infection. How does that explain the lower backache, knee pain and weakness in the legs?