Rash on belly?

I have a call out to his pediatrician already, and were told to just monitor and put A&D; ointment on. It is a weird rash that will go up and down daily. At one point it is basically gone, then suddenly it is back again. This has been going on since Thursday, and I am not able to figure out what is causing it. We have not changed our detergent, or fed him anything unusual, or had him around anything unusual. Here is a picture, and this is not at its worst. This is kind of in between. It is on both sides of the stomach, but right now the other side is not bad.