The last few days or so I've had a pain in my upper left abdomen, around my shoulder back. I thought it was muscle strain initially but it moves. It's around the area of my left shoulder. Sometimes behind, sometimes under. When I wake up in the morning it is more in my side (I sleep on my side). Googling it really isn't helping. I can't get to see my GP at the moment. What could this be? It's going to be something bad isn't it?