My 5 year old son has a weltlike rash on the left side of his torso. It has spread out from the initial site 5 days ago was the size of a half dollar now it is bigger than my palm and seems to be spreading into the groin area. He also has a runny nose cough and had a low grade fever for 3 days. The doctor thought it was a bug bite and gave us some antibacterial salve because of a small infection in the center of the site. Infection has cleared now this lingering rash. It is itchy and very red. And causes alot of discomfort especially at night. He has not been vaccinated for mmr. What could the rash be and how can we treat it?