It's not broken I know that much. I broke the left one a long time ago so I know what it feels like. But this feels similar in the right shoulder and also at the base of the neck. Gives me a stiff painful neck also. Had it for 3 days now and it's pretty bad. Didn't do anything particular I can recall other than played some tennis and threw some football over the weekend. Then this started on Monday night kind of suddenly while laying on couch watching TV. (Yeah, I know I should've been up and exercising instead. Must be couch potato syndrome. :) )
Have full range of arm motion and good strength. No sharp point of pain just in the general area of the collar bone more towards the base of the neck than at the tip of the shoulder and towards the back. Just a constant nagging pain day and night. No particular arm position makes it better or worth.