The first symptoms of mononucleosis typically include:
Unusual fatigue, such as the need for 12 to 16 hours of sleep daily
These symptoms are followed very shortly by:
Enlarged lymph nodes
Loss of appetite and slight weight loss
Nausea and vomiting (occasionally)
A red rash, usually on the chest. This is more likely if the person has recently taken the antibiotics ampicillin or amoxicillin.
Rare symptoms include:
Jaundice (yellow skin and eyes)
Irregular heart rhythms
In rare cases, an enlarged spleen can rupture. The spleen is a small organ near the stomach. Untreated, a ruptured spleen can cause life-threatening internal bleeding.