My lump was in my armpit where the SLNB was performed it was a "seroma" I went back to the breast surgeon and had it drained. It's pretty painless and almost instant relief. It did grow back and went back a 2nd time and drained it again. Maybe that's what you have? Finally when it felt like it was coming back I used a heating pad and voltaren gel on it. There is no lump now or swelling but that armpit area still feels really weird .