K.L.
Sounds to me like Roseola (or 6th disease). Its a virus that presents a high fever with no other sign of illness for a couple days that suddenly disappears. Then a red blotchy rash appears for abt 48 hrs. It doesn't it it just looks horrible. Its extremely common and just about all infants and toddlers get it. The good news is that once the rash appears the child is no longer contageous and they only get it once, then they are immune.