I have a pain in my back right under my shoulder blade and when I move fast it hurts bad but if i move very slow its ok, what could that be?

I got out the shower two nights ago and after I lotioned by body I layed back and stretched, when I sat back up i felt a bad pain under my shoulder blade in my back, I tried to strech it out I called the Dr. who told me to apply ice and wait until morning but still no change.