If you have shoulder pain, I think it has to do with your shoulder rest setup and its digging into your clavicle bone. This is just my professional opinion; you don't have to take my advice. From this video, it seems like it is set up much higher than your neck length. Your chin should loosely grip and relax on the chinrest by lowering the shoulder rest level. The violin should be able to flop around by its own when you take you left hand off of it when place in the right level. This will help you relaxed and not be as tense when you play. I hope this helps.
