My 6 months old has a rash

First time mom. My 6 month old has been sick since Friday with a fever and I noticed a little bit of a rash. I figured he was having an allergic reaction to the apples we just tried. I took him to the urgent care yesterday they said it was probably just a virus that is causing the rash and to let it run its course. The pictures on the top are from right now and the two one the bottom are last night. In less than 24 hours this rash has just gotten completely worse. It doesn't seem to be bothering him but it is completely covering his whole body, his butt cheeks and groin area is completely covered. I guess I'm just looking for advice or to see if anyone else has experienced this.