Does it feel like it is under your shoulder blade? Not the muscles on top of it, but under the shoulderblade itself? I get the same thing occasionally. I think its a pulled muscle under there. I usually put a heating pad on it for an hour or so, then I get in the shower and let hot water hit where it hurts. It helps if you have one of those jet shower heads that shoots the water out hard. A couple of tylenols before you do this usually speeds up the process.