As per your description, most probably the pain is due to 'dislocation of SC joint'. It is very difficult to diagnose it through X-Ray investigation. It is because, it's difficult to visualise it through X-ray.
It can only be diagnosed through clinical sign. All your clinical symptoms points toward SC joint dislocation.
As you said you get relief on rest, your only treatment option is to give complete rest to this SC joint. This can be acheived by using "figure-of-8" bandage.
Hope this helps you. Best wishes.
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