Small round rash on 5 month olds back?

My 5 month old has a small round rash on his back. it will seem to be fading or going away for several days then reappear. several people have told me it looks like a ringworm but im kind of skeptical because we have no animals and i am a complete clean freak so there really isnt any type of place he could have picked this up. especially on his back which is rarely exposed. i also dont know anyone else who currently has one and he is in my care all day every day so its not something he could have gotten from a day care or anything like that, he hasnt been away from me in several weeks. im not really all that concerned as it doesnt seem to bother him and is small but i wonder if maybe i should be more concerned? he has his 5 month appointment in a couple weeks and i have been watching it and was just going to ask then. did anyone else ever notice something like this on their child?