Thanks for your query,
As per symptoms mentioned,your son is having viral infection and rashes he developed can be a part of this illness and they are self limiting and need symptomatic treatment,
I suggest you to give acetaminophen
lotion on rashes 2 to 3 times a day.
Give him plenty of fluids and simple diet so as to maintain hydration and nutrition.
He should take adequate rest,
In case symptoms persist get him evaluated by pediatrician
Wishing your child good health