Thanks for the query.
The possible causes for your pain are:-
Abnormal posture at work like bending forward while sitting with out support to back, driving for long periods, holding shoulder bag like laptop bag, sleeping in lateral position, lifting weights by tightening chest muscles without balancing back muscles etc.
-Sometimes musculo skeletal problems like sub scapular injury
or fractured scapula etc can also cause this type of pain.
So you better once consult physician and undergo general examination which will possibly give clue regarding the cause for your problem then according to that specific investigations can be planned.
Dr Saurabh Gupta.