I Have Had Pain In The Area Of My Left

I have had pain in the area of my left shoulder blade for over a week. I think it started when I lifted a heavy bag and twisted something in my back. I have been taking Aleve or Tylenol for the pain. 2 days ago I called my doctor and got some muscle relax ors which I have been taking. The pain comes and goes, but is bothering me because it has gone on for over a week. Could it be something other than a muscle sprain?