I did something to my left shoulder over a year ago. Whatever it was would come and go for a while. I noticed discomfort most after doing yoga--a pose called chaturanga dandasana in which you begin in plank position and bend the elbows so that your torso lowers to elbow height. It also tends to hurt when I turn the steering wheel of my car with my left hand. As I was reaching back to put my arm through a sleeve, I could hear it crunching. A chiropractor suggested sprained AC joint. What did I do and how can I fix it?