Same thing happened to me ,a few times actually with both my daughters...........a doc told me it's good old mother nature alerting you that they are not well. After all the real little ones can't say what's wrong with them. My two used to get a rash up to about age 2 whenever they had a temperature / tonsilitus.
On the fith disease/slapped cheek note my daughter had this in june and it started with temperature ( i have never felt her so hot) and then one side of her face as red as a tomato she lost weight and could barely walk, she slept for almost a week. You done the right thing, I work in hospital and we would rather you came in than miss something. x