Would cortisone injection in neck/shoulder cause chest pains & infection 7 month after mastectomy?

If the injection sites were performed with sterile technique no where near your breasts and if you had no symptoms of infection otherwise, probably they did not contribute. 

Dear jrgrnthmb,What was the timing between the cortisone shots and chest pains? If you are experiencing chest pain now, you should go to the ER for a chest X-ray and evaluation. This is too potentially serious of an issue to discuss on an online forum. I wish you the best and please follow up.Best wishes,