Hi. If it keeps getting dislocated then there is definitely something wrong with the whole shoulder girdle. Start with physiotherapy and give it sometime. You have not mentioned how and where your shoulder dislocates so I am assuming anterior dislocation which is fairly common amongst dislocations. If no relief can be obtained from the physiotherapy then consult an orthopedist, you may need to undergo a procedure.

X-ray and MRI will tell you the cause of problems. There is no investigation apart from them except arthroscopy.

It may be due to poor posture..? If you correct your posture. It may gone within 2 months. So keep your elbows rest during table work, or riding, driving etc.