What Causes Pus Filled Lump Under The Armpit?

I had an bump that was filled with puss & blood under my armpit. I went to a doctor to get it drained & he gave me antibiotics for the infection and it closed up everything was okay . A couple months later a little bump appeared in the same spot but it didn t get as big as the other one & it popped it self and a whole was there and it took time to heal , and now & then a hole will alway appear under there & close back up .