My sister-in-law had terrible back pain on chemo (and ended up in hospital after each session) and had to stop chemo after only two of her planned four treatments. She didn't require radio but has just finished heceptim (not sure how to spell that) She had a double masectomy and is doing very well. We are all different and the cause of her pain was never found. She has a very sensitive system and the chemo just did not agree with her. Trust your specialists you can be sure this has happened to other women so they will know what to do. Take big big deep breaths, sounds silly but this will help calm you down as you are going through so much at present.
My thoughts are with you, keep us posted.
Anne-Marie