My baby got sick.

My baby boy has had been running a fever for the past 3 days, and when the fever has been reduced, his body begun to show a red rashes. His doctor said the rash is called "Roseola", it is not itchy and he will not feel the itch urge to scratch it. It's very common among babies and it most likely will only appear once in a lifetime appearance.

A few points, In English, you can not say had running, as had is past tense and running is present tense. You can either say Had a fever or has been running a fever

We do not get more than one rash at a time. ( It would be very rare to have rashes.) If you had rashes, you would have to have two very obviously different types of rashes. Your baby I assume just has the same rash all over, so we say a red rash