Yes, this is more common than people realize after mastectomy and even more likely if you have had an axillary node dissection.
I am surprised that the surgeons and doctors havent heard of this, and it's called:
Post-Mastectomy Pain Syndrome (PMPS)
Google this and you can see everything from causes (which is primarily due to damage to the nerves during the operation) to treatment.
I recommend you move forward into getting this pain officially recognised as soon as possible. I suffer also from this but got a little pusht when mu surgeon also told me he "hadn't heard of it"
I am now able to fully exercise almost back to the normal movement of my good arm, only now, some 3 months later, able to bear wearing a bra over the area and feel I am doing very well - but this was possible only due to having adequate pain relief that allowed me to regain quality of life
Good luck
I personally did not and I don't recall anyone mentioning the specific pain that you are experiencing. Often there is some nerve damage that occurs during Mastectomy but most times this doesn't last as long as you have stated. I'm not sure which Dr. "doesn't get it" .... Surgeon or Oncologist. It seems that at least one of them would investigate the problem. I hope you are having routine screenings for any sign of recurrence .. scans in particular. I would advise that you have a serious discussion with your Oncologist and if all tests are negative then perhaps you should make an appointment at a Pain Clinic. They have excellent investigative skills and have various methods of pain control to offer. Regards ...