How concerned should I be for my 19 year old son with an extreme rash related to being on antibiotics while having mono? Antibiotics started 7 days ago prior to diagnosis of mono--negative for strep at time of mono diagnosis, but Doctors said to keep taking the amoxicillin. Rash began 24 hours ago, improved minimally with antihistamine s, stopped amoxicillin 12 hours ago, per doctor verification of cessation. Rash has worsened, completely covers trunk, face, ears, now spreading down torso. Not yet on legs or feet. No sign of rash within the mouth or swelling of tongue or airway. Thanks for any direction.