Suggest Remedy For High Fever With Rash On The Body And Headache

My Grandson who is 4 1/2 had high fever last week that spiked to 103.5. He was taken to the pediatric hospital E.R., and they gave him Tylenol suppositories and released him when the fever came down. Once home, the fever spiked again, and he developed a rash on his trunk. [small pink hives, almost like heat-rash] he complained of a bad headache. After Tylenol through the night the fever subsided, but today he was pale, complained of headache again and threw up on the trip to the doctors. They said it was viral and to keep him hydrated and continue with the Tylenol. Is this just a common virus, or could it be symptomatic of something more serious? He s lethargic and keeps complaining of the bad headache.