Mononucleosis is a viral infection causing fever, sore throat, and swollen lymph glands, especially in the neck.SymptomsMono may begin slowly with fatigue, a general ill feeling, headache, and sore throat. The sore throat slowly gets worse. Your tonsils become swollen and develop a whitish-yellow covering. The lymph nodes in the neck are frequently swollen and painful.A pink, measles-like rash can occur and is more likely if you take the medicines ampicillin or amoxicillin for a throat infection. (Antibiotics should NOT be given without a positive Strep test.) Symptoms of mononucleosis include:DrowsinessFeverGeneral discomfort, uneasiness, or ill feelingLoss of appetiteMuscle aches or stiffnessRashSore throatSwollen lymph nodes, especially in the neck and armpitSwollen spleenLess frequentl