I Have A Teen Son, Age 14. He Has Been

I have a teen son, age 14. He has been sick with a mild flu for the last week And has been sleeping a lot. Yesterday he felt better for the first time in a week. This morning I notice his hands where very red, he said he had a headache and was going to go lay down, When I checked on him several hours later he has a rash all over his face arms and torso. I Gave him Benadryl but it has not worked and he has slept all day.