Pityriasis Rosea vs. Fifth's Disease

Adam developed a rash about a week ago on a Thursday. It started as tiny spots on his chest. By Friday it was redder and had spread to his back and groin. By Saturday he had large splotches on his under arms and chest:

At this point we called the pediatrician and went in to have it looked at (luckily our pediatrician has Saturday hours). The Dr. consulted some of her dermatology books and pronounced in Pityriasis Rosea, a rash caused by a virus. It isn't contagious and goes away by itself in 6-10 weeks. So we went home. Saturday night was rough. Adam had a fever and was scratching like crazy. The rash was worse the next day and Adam felt awful. My favorite quote from my normally rambunctious boy was, "Mama, I not happy" said in the most pathetic voice possible.

Fast forward to Wednesday. Adam is feeling better and the rash that was supposed to take 6-10 weeks to go away is gone. I was talking on the phone with a friend whose son Adam often plays with and she mentioned that her son was just getting over Fifths Disease. She described the symptoms and they sounded suspiciously like Adam's. Looking it up online, however, it didn't exactly fit. For example, Adam got a rash first and then felt sick. With Fifths Disease the rash comes after the illness.

So anyway, we're not sure what it was. It wasn't fun, but it's over, thankfully in less than 10 weeks.