A female bully of mine from years ago had an awful infection same way, it smelled horrible but I had just gotten her and was in another state driving back. She was so cute and it hurt you could tell. I took her in for her puppy check up which is where they told me what was wrong. They gave me meds and said to soak her bottom daily and just pat it as to not cause her to hurt from drying. I did this daily and the meds helped and took her back and she said it was all better. I had to do this for a week straight. My concern was the moisture from the daily soaking but it went away using a medicated soap. First time experiencing this but it was nasty smelling and a greenish color. Ewe! But thank goodness for the vet pointing that out to me.