What Causes Frequent Popping And Cracking Of Shoulder?

About 2 years ago was the first time my shoulder popped out of place. It's happening more frequently and it happens when i do activities like swimming, basketball, it happened once while I was sleeping and it hurts when i take my shirt off. Also, whenever I put a bag on my right arm (its my right shoulder) it feels like my shoulder is being pulled down. It always cracks whenever it moves. I went to the dr and he is sending me to an orthapedic surgeon. I'm 15 , right handed and fairly active. What will the orthapedic say or do for my shoulder? What is wrong?