What Causes A Sharp Sudden Pain Under The Shoulder Blades?

I have had a sharp sudden pain under my right shoulder blade today. It has happened after meals and when bending down, lifting books, getting in car. It steals my breath when it hits. The spot is not sore to pressure. I did shovel snow earlier this week, but the soreness ended three days ago. Wondered if it was possible to be gall bladder instead of muscle strain or something?