Can Poor Posture Cause Shooting Pain And Numbness In Neck, Shoulders And Forearm?

I play guitar for many hours a day and have been experiencing pain starting from my neck, across the left shoulder and down my forearm. Also there is swelling or puffiness next to the left neck area. This all started over 5 years ago while playing and felt a sudden shooting pain, like an electrical shock, beginning from my left neck area all the way down to my fingers in left hand. Fingers felt numb for over 30 minutes and loss of strength in left shoulder area. I ve had a cortisone shot in left elbow area that did relieve the symptoms but I know this is only a temporary solution. I ve always had poor posture since I was a child and think this contributes to my problem. Any suggestions would be helpful. Thank you.