It does sound like ringworm , especially with the normal-appearing skin contained within the circle of the ring.
We were dx with ringworm 2 weeks ago. Family doc said Lamisil cream, which is now OTC. You can find it with the athlete's foot stuff. Dr said if it doesn't respond in 2 weeks, we can try an oral antifungal.
TBH, I have done SOME natural stuff, but not enough to actually treat it. DH and I share parenting duties, and DH is not concerned in the least about using natural things. (coconut oil, lavendar oil, ACV, TTO are some things that will treat fungal infections on the skin) In fact, he is suspicious of them. (not suspicious like, "I doubt they will work." suspicious like, "They may do harm..." ugh). I did use a bit of CO, ACV, and TTO - CO after the bath, and ACV or TTO in the bath. Did not think to use ACV directly.
The fungus IS responding to the Lamisil. I would almost rather have him use an oral antifungal, as I suspect some problems with yeast. He also has/had tinea versicolor, which is another fungus. His abdomen is covered with tv spots; his butt and thighs are covered with ringworm spots; his calves have either one or the other, I can't tell. He has brown skin with all these white spots. It's not pretty.
DS, 10/07. Allergies: peanut, egg, wheat. We've added dairy back in. And taken it back out again. It causes sandpaper skin with itchy patches and thrashing during sleep. Due w/ #2 late April, 2012.