I have cording in my armpit from surgery and radiation over a year ago. It is better then 6 months ago, but I do not have the pain you described. Mine is more of a stiffness when I do exercise that involve raising my arms above head.

Here is additional info on cording:
https://www.breastcancer.org/treatment/side_effects/aws.
Also, here is link to a discussion on cording on Mayo Connect:
https://connect.mayoclinic.org/discussion/cording-axillary-web-syndrome-aws/
Laurie