Jul 21, - What are the symptoms of mono? a fever. a sore throat. swollen lymph glands in your neck and armpits. a headache. fatigue. muscle weakness. swollen tonsils. night sweats.Symptoms · Causes · Diagnosis · Treatment. Mono Symptoms in Adults: Infectious mononucleosis (mono), a transmittable sickness, is caused by a herpes virus called Epstein-Barr virus (EBV) that attacks.