What might be the cause of severe pain under left breast during and after sneezing?

I had a bilateral mastectomy in October, 2014 and presently have tissue expanders. This was treatment for DCIS and no further radiation, chemotherapy, or Rx therapy has been required. 3 days ago, I strained a chest muscle while dancing (yes, I'm older... 50), and 2 days later I began experiencing excruciating pain under my left breast and down my left arm when I sneeze, cough, or blow my nose. Sneezing it the worse and leaves me sore for a half hour afterwards. Should I be worried that something is amiss with the expanders?