This is well-documented in children who take amoxicillin while infected with the Epstein-Barr virus that causes mononucleosis ...

“Many people have the Epstein-Barr virus (EBV)—the main viral cause of mononucleosis ... a rash after taking an antibiotic ...

Amoxicillin 1000mg ... Monitor closely if skin rash develops; discontinue if lesions progress. Evaluate if diarrhea occurs. Avoid in those with mononucleosis. Hepatic impairment: monitor.