Wierd Virus

All was pretty normal yesterday until we went to bed. Nathaniel and I had a play date and lunch with some friends, I took care of work and did some house cleaning. Chad came home in the evening in time to play and hang out with us for a bit before it was time for Nathaniel to go to bed. I put him down about 8 pm. At 11pm I heard him yelling for me in his room. This normally means he wants a drink of water or has kicked his covers off. When I went in his room he was crying saying his legs hurt so I rubbed them and asked him where. He said all over and that they were itchy. I turned on his light and stripped off his PJ bottoms only to see my kid covered in red bumps behind both knees and on the tops of his thighs. I woke Chad up so he could help me decide what to do. I ended up putting hydrocortisone on the bumps and inspecting the rest of Nathaniel's entire body. He had other cluster bumps on his arms too. The last place I wanted to go was the emergency room so I decided to wait and give the cream a little bit of time to work. He had no other symptoms, no temp, no runny nose, no congestion, no coughing, nothing. After a few minutes of having the cream on Nathaniel said he felt better and wanted to go back to sleep. I was worried to let him stay in his own bed alone not knowing what we were dealing with so I put him in bed with us (guess there is a first time for everything - he has never slept with us). He eventually fell asleep and I didn't really sleep at all. I impatiently waited for him to wake up this morning so I could see how the bumps looked. To my surprise when he got up there was nothing to see, completely gone and I was confused. Until I looked him over and found new bumps in other areas of his body. He had some on his neck and arms that showed up at 6am but by 8am they were gone. Next he had them on his face and stomach. I took him to the pediatricians office first thing this morning only to find out that he has a virus! Not contagious (that time has already passed) but the bumps will continue to move around his body and itch for anywhere between a couple of days up to a couple of weeks. We continue with the hydrocortisone and use children's Benadryl when needed. He seems pretty comfortable now and as the bumps move I keep applying the cream to help keep the itchiness to a minimum. I am glad I know what it is now - I had suspected either an allergic reaction or virus and at least with a virus I don't have to try an figure out what he ate or did that may have caused the allergy.
Not a good picture because last night it never crossed my mind to take a picture (too concerned for my kid) but this morning when I noticed the bumps moving around I did get one of his arm.