Roseola rash

My 11 months son had a running nose last weekend after few days he is coughing with running.nose and some rash on his neck and arm. Then he is down with high fever going on and off for 3 days to 4 days. Now recovering from fever, he body rash flare and spread to his face and body. I am wondering what I can i do to help him ease the itchiness and discomfort?