Well, without a clinical evaluation it would be difficult to determine the cause of your symptoms. Possibilities include inflammations like arthritis, capsulitis, bursitis, tendonitis; muscle sprain, muscle/ ligament/ tendon tears/ injuries, fractures, nerve impingement/ compression, growths/ masses, ischemia etc. I would suggest an evaluation by an orthopedician for an accurate diagnosis and appropriate management. Meanwhile you could try resting the shoulder. Warm compresses and NSAIDS may be useful for pain relief.
Hope this helps.
I have had the same problem for one year next month. Started with shoulder, shoulderblade and arm pain on the left side. After a bull crap shoulder surgery and test after test the doc's found out that it is a disc in my neck that is pushing on nerves. I went through lots of treatments (pt and injections) and am now to the end of the road and need surgery to fix it.
Now days I feel pain between and under both shoulder blades, arms, elbows, neck. Heat feels the best to help relax the muscal that are in spasms due to the pressure on the nerve. But I have been told that ice is better (to help get swelling down.)