You are understandably distressed about this pain. Any time anyone develops symptoms near the site of an old tumor, there are worries about recurrence of that tumor. The best physician to approach about this issue is the oncologist
you saw for you breast cancer.
Pain can be caused by tumor recurrence in certain situations. Most of the time, pain at a former surgical site (after it has healed) is due to nerve damage from the operation. This pain can occur weeks to months after the site has healed and sometimes can take longer. We call this neuropathic pain. Usually when breast cancer comes back, it does so elsewhere at distant metastatic sites such as the bone or lung.
The more important question is what your individual risk of having the tumor come back. This is determined by how many (if any) lymph nodes were involved, and if all the tumor was removed. From there, you should have a surveillance schedule in which you get checked out routinely. If you are following through with these checks, then you are reducing the risk that a recurrence would go undetected.
I suggest that you schedule another appointment with your oncologist. The two of you can discuss what appropriate screening tools are necessary for particular stage of cancer (at diagnosis). This way you can be more able to appropriately respond to symptoms you have as they come along. Good luck.