Hi Kat,
I finished chemo on 23 May 2013. In July I began to feel pain in my surviving breast, and what felt like lumps. My oncologist advised me to get in touch with my BCN and ask her to get me an appointment at the breast clinic. She did, and I had an ultra sound on good breast. Nothing was found, but afterwards the nurse asked me to lie on the opposite side to my good breast (onto the side of my mastectomy). She put her hand at the top of my ribs, just at the side of my breast, and pressed down hard. I yelled and almost jumped off the bed. She then told me the pain was caused by Costochondritis, inflammation of the ribs. It causes pain in the breast, and can sometimes be so bad it feels like a heart attack!! Needless to say I was sent home reassured. The pain has since moved over to the mastectomy side ribs but I've been told it won't last forever, so I just take Ibuprefen. I don't know if this rings any bells with you. Try pressing on the top of your ribs (or get OH to do it) and see if that is painful - if so, chances are it could be Costochondritis. It is very common.
poemsgalore. xx