Oh, Kath...I knew you had shoulder pain but I didn't realise how bad it had become or how difficult it was being to get some answers. I'm so glad that you have had an MRI now because at least you can rule that out. It sounds like your rheumatologist is on the ball. Is he in Adelaide or down your way?
I'm currently waiting to see if treatment has triggered an auto-immune response, as well, just to cover all bases. Onc told me a couple of weeks ago that the severity of my joint pain was making the Letrozole unsustainable and put me on a week of prednisolone which worked like someone had waved a magic wand. I guess it's only a short term fix, though and it will come back. Has prednisolone been suggested to you? I gather it's a step up from painkillers. The onc's immediate response to my answers to his questions about the joints was that it was inflammation almost certainly caused by the Letrozole - so it's obviously well known that it can have such a detrimental effect. (He also didn't argue when I said that I'm sure you guys say 5 years on it because 10 would be too overwhelming.) I completely understand your fear of going off it even though it's causing so much pain. I'm not even keen to switch to Tamoxifen as it had no impact on my sister's cancer (I know the circumstances and timing were different but I just can't get my head around that).
I hope that now you have someone listening to you, you get the quality treatment you deserve.