Bad rash

My son went to the dr Wednesday with high fever, cough, runny nose, & tugging at ear. He would eat anything either. Strep & flu negative, dr said he had ear infection. He started on amoxicillin Wednesday night, Friday he is covered in a rash head to toe. He is completely miserable & whiny. He won’t hardly eat & has a wet cough. No fever though. Does this rash look like an allergic reaction? Calling dr first thing Monday morning. Our urgent care doesn’t see kids under 2