Full body rash? Just viral?

Looking for advice about this rash on my 4 yr old son. So being sick started on Friday with fever and throat sores. Saw the dr, tested negative for strep and covid. They said it's viral. Sickness continues through the weekend. Monday the rash starts and turns into a full body rash. I thought it was hives at first. No new foods, detergent, medicine. Nothing new. After hours ped had us go to er, who very quickly said it was a viral rash and it will go away on its own. They gave us an antihistamine. Its Wednesday now and it hasnt gotten any better. Still all over. Fevers on and off. Itchy at times. Still has throat sores as well. I will include pictures from today. Any advice? Wait it out or should i be contacting the dr again?