What Causes Persistent Pinching Sensation In Back Post Injury?

Good evening, I'm an 18y/o male who recently injured my back. I'm very active and play basketball 3-4 hours a day. I recently began lifting weights 5 months ago and thought I was very careful on how I position myself prior to lifting. I begin feeling a pinch in my left trapezoid in my back for the past two weeks and its very painful. I went to the ER department at the local hospital and they gave me a muscle relaxer, trimadol, and two shots of robaxtson. I had a little relief, but it continues to cause great pain. I'm not able to look down or lay down in certain positions. What can I do for relief?