I noticed that some of your responses are a bit alarming, so I thought I would add my own experience which is not. It's good that you're taking him to the doctor, though, just to be safe. I and my daughter (who is 3) have both experienced various strange skin issues. I guess they would fall under the basic heading of eczema. My daughter will periodically get a strange breakout of red rash, mostly on her legs. It is mild, and I have found that it usually goes away with a generous and steady application of Aveeno baby lotion. Until you see the doctor tomorrow, I would not use the antifungal cream, since that seems to be irritating things. You might try 1% hydrocortisone cream, which we have also found helpful at times. It is very mild.
I should probably also mention that a few years ago, I myself developed an unusual rash called pityriasis rosea. It is an annoying rash that begins with a "herald patch," similar to the spot you described. Then it spreads to the trunk and legs and goes away on its own in a few weeks. It is not harmful, just annoying. Generous applications of baby oil after a lukewarm shower were what got me through it. Just thought I would mention it, since it is not something you hear about a lot, but you never know. Good luck, and I hope that your son's issue is something mild.