I also have these same symptoms. Sharp pain lasting a few seconds, mainly on the right side of sternum but sometimes moves to the left. I also have pain inbetween my shoulder blades. My doc seems to think its muscular and has set me up to try physical therapy. It doesn't FEEL muscular as I can't make the pain. But there are times when I press on it and it hurts. Sorry I have no answers for you. Just wanted to let you know you're not alone!