Terrible Rash!

My 17 month old has broken out in a nasty rash recently. He has no fever or really any other symptoms other than irritability and loss of appetite, the rash however seems to be spreading by the hour. He went to the doctors yesterday and she told us that he has a virus and it should clear up in 7-10 days. But she didn’t tell us what virus she thinks it is and didn’t offer really any relief or further explanation. I’m wondering if anyone has seen this before and what was the outcome or what caused it. Thank you in advance!