Looks like you have unstable shoulder. You will need to be investigated for it. First a X-ray of the shoulder will be required to rule out a fracture of the shoulder cup (glenoid), the a MRI of the shoulder will be required. If there is a tear of the cup rim (labrum) then with key hole surgery it can be fixed. But I would like to know how many times have you dislocated your shoulder?
Next Steps
Should visit a arthroscopy/sports injury specialist
Health Tips
Since you are very young a surgery will be required as there is a high chance that without it you will keep dislocating your shoulder.