I Am Ten Years Out Of Stage 4 Breast Cancer

I am ten years out of stage 4 breast cancer with a mastectomy done in 1991. I have had an increase in a strange symptom. I have a spasm in the chest, abdomen and/or diaphragm that is very painful. I am current on mammograms & had a MRI of the chest in '10. Should I be looking at some other cause if this? It seems to be getting worse. I am 63 and in fairly good over all health. I exercise ui& eat nutriously.