It could be impetigo (staph.)
In my experience, it has been hard to combat...my DS has recurring staph infection on his diaper area. I've tried herbal sitz baths, goldenseal, herbal ointments, etc., oral abx, and abx cream. One of the abx creams we used worked but was $100.
Because they are recurring, I have come to the conclusion that it is more an issue of the immune system than it is the bacteria itself.
I've started giving him 2 doses of probiotics per day, echinacea each day, plus giving him daily baths with GSE, washing diapers and towels with GSE and swabbing his diaper area with the GSE mixed with water as well as using the abx cream for the rest of the treatment time.
Once this session of the infection is over, I will continue to wipe his bottom with GSE because he has eczema so I'm hoping it will help keep it cleaner.