Without an examination I am unable to be sure, but I think you have a frozen shoulder.
Lying on your back with shoulder and elbow at 90*, upper arm pointing to the ceiling, rotate your shoulder in and out. Do it first with the good arm, and then the naughty arm. Is there a marked difference in internal or external rotation? Limited and painful.
It's one of the most painful and debilitating conditions. Read more at Frozen Shoulder ...
First and foremost, start our Frozen Shoulder exercises, do them faithfully every single day. Several times.
The problem usually lies in the acromioclavicular joint, the first rib or a lower cervical facet.
Seeing you have pain in other joints, rheumatoid needs to be considered, and a deficiency of magnesium that causes chondrocalcinosis. Spinach is the best source, but you make no mention of calcium seen in the shoulder on the X-ray.
Lastly I'd start taking fish oil, and /or freshly ground flaxseeds for the omega-3.
Good luck, this is a very painful condition.
Dr. Barrie Lewis