Dislocated my right shoulder in january of 2013, reduced, slung it with pt. My right collarbone looks different & right side of neck feels tense. Why?

Dislocation ? After a shoulder dislocation and sling immobilization disuse atrophy of the shoulder muscles can occur and cause the clavicle to appear more prominent. Also, with more scapular than glenohumeral( sh. Jt.) relative motion occurring your trapezius may be seeing more motion and " tenser"... Of course, an acromioclavicular "separation" of the shoulder can cause these 'changes' more quickly...