I had a small tumor took out of my left breast feb 6, 2015, I then had 10 redation treatments in march, 2015. For about the last 3 weeks my breast is sore and sharp pains shoot through it. There is a very medium hard knot own the place of my surgery. I have to take Tylenol to control the pain. Can you please tell me what may be causing this, Thank you, marsha Balentine