I had this as a teenager on my upper right arm, fortunately the fungus did not spread further. The doctor told me to get an athletes foot cream with Miconazole in it, the growth disappeared in less than two weeks, although I had white blotches all summer before the skin pigment returned.
Since this is a fungal growth I would suggest you use oil of oregano or tea tree oil (or both) on the lesions, then for extra protection also take a few drops of oil of oregano or GSE (grapefruit seed extract) internally for a period of time. Apparently the yeast is always present, but something triggered it to become fungal in nature and grow into the skin surface. I do not think its a systemic fungal growth like Candida, but effect the skin much like a parasite.