Hi,
Sorry for what happened to you. Lots of us feel the same, which means you are in the right place to vent.

Ok, you need to get your docs to refer you to a very good physical therapist--Christine's thought as well, but also one who works with head and neck patients.

You'll see I had the same surgery, but one bad lymph node so add radiation & chemo to the mix, which generally makes the after effects worse. But I did not experience the shoulder pain, except for maybe some twinges early on. Nevertheless I got a referral to a PT, which I consider one of the smartest things I ever did. She had me on a lot of exercises as my neck was so weak. I also learned lymphedema massage, which only some PTs are qualified in. I still use the lymphedema massage now. I still do the exercises for head and neck now.
You will feel so much better about yourself if you do this.

Doctors are not very good about being proactive with physical therapy, so you ask, and do not take "no" for an answer. You need to get on the better of side of the shoulder pain, and the exercises you do now will benefit you down the road.

Best,
Anne