Hi Kenzi ~
Sorry you are still having problems despite the PT. You said some things improved - that's good news. You and so many here have multiple issues in the neck so it's hard to know what's causing what sometimes.
YES, it could be caused by your disc & cord issues. I saw my PM doc last week and he feels my new arm symptoms (bilateral) are likely the disc compressing the cord. Whether it is just with certain posture or movement - we aren't sure yet.
I've been thinking about your question for days. You mention the fatiguing of your right arm when reaching up. Do you get the weakness with your arm in other positions (like when typing etc) ?
Just a thought... Since your problem is only one arm, I am wondering if you might have Thoracic Outlet Syndrome on the right. You might google it. Usually the symptoms, in your case - weakness
, is reproduced when the arm is extended in front of the body and raised up. Kinda like you described reaching up to put dishes away.
I hope you find an answer soon - at least at your appt. on the 11th. Just wanted you to know I'm thinking about you.