Re: Rash and Fever in 4m old??
It sounds like Roseola. It starts with a high fever and no other symptoms for a few days. After the fever ends a rash starts. The rash lasts about a day and then goes away. They are very cranky that day. When ds1 had it, he was up all night and wouldn't sleep.
With fifth disease usually by the time the rash starts they aren't contagious anymore. When they are contagious they may have fever or no symptoms. It looks a lot like a sunburn on the cheeks and arms. When ds2 had it this year, I thought he was getting sunburned at school during recess at first because he is very fair. My dc actually had the symptoms in the reverse order and got the rash first, and were then feverish for a few days.