Thank you for your query.
Viral infections are known to produce rash
after 2-3 days of fever
which appears in your son. In most of the cases the rash appears as the temperature normalizes. I suggest that you can wait and watch. However to be on the safer side get him examined by a doctor and do the basic investigations as suggested by him.
I hope I have answered your query to your satisfaction.
Wishing your son an early recovery.
Rajiv K Khandelwal