It has been quite some time since your surgery.
Nothing can be said with surety but this could be pain due to scar tissue formation.
Do you notice any abnormal feature like breast lump, skin changes or nipple discharge on breast self examination?
What is your age?
It would be best to consult your doctor for a clinical examination.
Till then you could try some warm compresses, local analgesic creams and oral pain relief medications.
Let us know how you are doing and if you have any other doubts.