DS had exactly the same thing a week and half ago. He'd had a little bit of a cold, got an ear infection, then just as that cleared up and his temp went down he broke out in a rash that looked like german measles to me. I took him back to the GP and she told me that it was to do with the virus he'd had, it's the body having a reaction to it and it shows that they are no longer contagious and that it is nearing it's end. His was pretty much gone the next day, all up I think he had it for only about 36 hours. HTH