Thanks for putting up your query over here. Persistent sore throat with fatigue can be due to some possibilities which need to be ruled out on basis of following symptoms- Yes,there is likeliness of infectious mononucleosis,but as you mentioned you have got the blood test negative for it,the test can be false negative in initial period of illness,so it needs to be repeated after 10-14 days. Presence of persistent fever ,decreased appetite or discomfort while swallowing usually seen in bacterial tonsillitis and other infectious origin.Certain basic blood investigations and nasopharyngeal secretion cultures needs to be done followed by antibiotic course under physician s supervision.If cause is recurrent bacterial tonsillitis,surgical intervention can be done. Do you have hoarsness of voice, or foreign body sensation in throat ?If yes,it points to laryngeal problems diagnosed on examination by an ENT surgeon. Are you on any medications or immunosuppressive drugs like steroids? Even chronic smoking or exposure to dust and environmental pollutants may cause this scenario you have,so you need to take steps on that aspect like avoiding exposure to smoke or environment pollutants.In that case,may I know what your occupation is? Have plenty of fluids,enough bed rest and salt water gargles. Thanks and regards.