To answer your question regarding the rash, usually this is the virus releasing the toxins after the illness. If the rash diasppears altogether then reappears I would be more concern with secondary infection or a type of dermatitis. First, see how your child behavior is as far as eating, drinking, acting playful. Is your child behavior the same? What is the child's temp? >38.5c is a concern. IS your child sleeping all the time? If he back to acting his normal self, I would just monitor for now. But if there is a temp, change in loc(level of consciousness/alertness) I would take him to the doctor. Here is two methods of soothing as listed below. Be careful of othe products you use because it could irritate the rash. And remember if you are still feeling uncomfortable with your child take him to the doctor. Its better to be safe then sorry later.

Calamine lotion or oatmeal bath( 2 cup finely grind oatmeal add to bath water) for soothing the itching.