Go to the doctor and make sure its not something heart related. Better to be safe than sorry. If it isn't that, it may be sitting for a long period of time and being somewhat hunched over- the position stretches your muscles of posture too much and can be painful. I would suggest trying a physical therapist to assess your posture, strength and endurance with activity. Chiropractors can help to soothe the pain but the physical therapist can help with the origin or cause of the problem.
In today's society with computers, desk jobs and lack of excercise, many people seem to be getting arthritis pain at earlier ages. It sounds like you have joints that have formed along your thoracic spine area. I'd suggest trying a chiropractor and if still having pain, get an MRI done. Good luck!