mystery rash

Last week Trent got a little rash on his right hip. We didn't think much of it and I put some diaper cream on it. The next day it was a little bigger, but still nothing to worry about. Then daycare called and mentioned it, and I decided it was time to take Trent to the doctor. We got in that day and saw the doc, who could not identify the rash, which was now red and raised with tiny blisters all over it and extending from his hip up the side of his torso about 6 inches. The doctor told us to bathe him twice a day with Dial soap and to call him the next day to let him know how it was looking. It looked bad. Had spread quite a bit. Anticipating that he'd advise us to see a dermatologist I made an appointment before speaking to him. The dermatologist narrowed it down to 3 possibilities, 2 viral and 1 bacterial. She took a swab and sent it off for testing, and in the mean time we would treat it for a bacterial infection with a topical antibiotic and a steroid. It took about 3 days of that to get the rash under control and meanwhile it had spread over to his butt cheek and down his right leg.
The surprising thing in all this is that it didn't seem to phase Trent at all. He never scratched it, and he never indicated that he was in pain or that it bothered him. He was marginally irritable on Thursday after we took him to the pediatrician, but beyond that he was his normal, charming self.
Yesterday, the last time I saw the rash, it was looking so much less angry and the blisters had turned into tiny red scabs. This morning the dermatologist called to tell me that the tests came back "normal". I asked her to clarify what she meant by "normal" since it could mean that it was an expected result taking the symptoms into consideration. However, she clarified it to mean that there was no virus and no bacteria. I should be relieved, right? He doesn't have a virus, and his skin isn't showing any signs of a bacterial infection, such as staph. But I'm not relieved. I want to know what it is. Of course, when the rash became a concern I googled it and found many sites with descriptions and pictures, none of which matched exactly. Some pictures of shingles matched, but the description didn't. And the way you get a bacterial infection, such as staph didn't match either. Usually you have to have an open wound that gets exposed to staph, and Trent never had a scratch on him. It's just so puzzling and frustrating.
Since the rash is responding to the current treatment, we'll continue to use it. And we see the dermatologist next week again so I hope to get some better answers.