My 17 Year Old Son Has Had Cold Like Symptoms

My 17 year old son has had cold like symptoms for about 3 days. He now has a rash in his throat. It is inflamed but not terribly swollen but has small white dots. Today he has developed bumps and pain throughout his mouth as well as mild swelling of his tongue. He had a high fever on day one but has not had one today. He has no skin rash but has had some nausea and diarrhea. He also had Impetigo last week which is being treated with topical antibiotic ointment. I feel like this is viral but am wondering if he needs to be seen. His younger sister had similar symptoms last week but tested negative for both Strep and Mono.