Suggest Treatment For Rash In Armpits

I am a 50 year old black female. I have diabetes and high blood pressure. I am 5feet 5 inches and fairly excersise. I eat pretty health. I notice at one point I would get musty under my arm, afterwhich I gor bils under both arm pits. I still have a rash under one of the armpits, but I do not get musty anymore. I have not used deodrant in a couple of months. I went to the doctor and he gave me antibotis. I am almost finished with these, still feel a knot under the skin of my right arm. what should be my next step and who to consult with.

KB