Viral infection (fever then rash)

My son is 9 months old and he had a mild fever for three days.
We gave him Baby Tylenol and the fever went away.
However, after the fever, he now has a rash. A doctor friend of our
family said that it is probably a viral infection.
The rash is now all over is body (from head to toe).

I would like to know, how long does the rash usually last and what should I
do to sooth his itchiness? Is there a cream I can apply?


Please reply as soon as you can.