Hello, Welcome to Health Care Magic. I read your query and I understand your concerns. Yes, this rash be from the mono virus. The common symptoms usually consist of fever, pharyngitis, and lymphadenopathy, but sometimes a rash could be present. Mono rash is a common symptoms experienced when affected with mononucleosis. It usually develops on 7 to 10 days after treatment with beta-lactam antibiotics such as ampicillin, amoxicillin and cephalosporins. Typically this rash is tan or brownish in color. Since the color is quite different than the typical very red allergic-type rash, this should not be misinterpreted as a penicillin allergy.If such rashes appear then it is a clear indication of hypersensitivity reaction to antibiotic. However, this is not a real allergy and does not mean that the person is allergic to such medications. This rash indicates a ‘hypersensitivity reaction’ to the antibiotic. If the antibiotic is given later on in the absence of EBV infection the reaction doesn t occur, so it is not a true allergy. However, because the shape and distribution of the rash of infectious mononucleosis plus antibiotics are similar to an allergic-type rash, they could be often confused by patients and clinicians. Hope I helped with my answer. For further concerns or follow up questions, don t hesitate to write again. Take Care, Dr. Ina