Hello. My Name Is Dyanna. My Son Is 6 Years

Hello. My name is Dyanna. My son is 6 years old. He has had a fever for 2 days now, he said his back was hurt and ached all over. Then he got a rash that itches all over his body. He is now complaining he is cold. We now are giving him Benadryl. What do you think it might be and should I take home to Dr. ? Thank you