Dear Ispvideo, You should have your surgeon take a look at this who can evaluate this in context of your situation.
As SueYoung55 thinks, my first response would be surgeon as well unless it has been some time since your operation? I would see both or the first one who is available, or call your oncologist and let them advise you after what you told us?
This could be something more serious, lzpvideo. I cannot make a diagnosis, and the experts won't make one for you, but hopefully both I and they can steer you in the right direction. You need to be checked out soon. Katrin
Surgeon. How long ago was your mastectomy? If it wasn't long ago it may simply be a case of your drain coming out too soon. Needle aspiration doesn't hurt and could offer you some relief.