I'm a 17-year-old female. Just recently, about 5 or 6 days ago, I've been experiencing shoulder aches/burns, I suppose. Not directly in my shoulder, but more on my upper back/shoulder blade. On the left side. It's been going on for 5-6 days so far, and at night it's the worse, and when I wake up, no aches or burns. Is this a serious problem or what exactly is it?