I have found from listening to others' stories and from personal experience that they can be caused by an allergy. Often, it is a food allergy. You may want to consider a change in food if they are re-occuring. A change in protein can be a good start. I used peroxide but I think, if I had known, I would have done epsom salt as well.
For yeast, you can do a 50/50 mix of apple cider vinegar and clean the area. That can often help as the acv kills the yeast. However, the yeast is a symptom, again, usually of an allergy.