I have sharp pain under left shoulder blade every few hours for only 5-10 seconds. First, it hurt to take a deep breath although I could. Now, it does?

Sharp pain. This most likely is a pinched intercostal nerve or muscle that runs between 2 ribs. It causes Sharp, fleeting pains often precipitated by a deep breath. A lung cause or pleurisy is also a possibility if there is associated cough or fever. Pinched nerve is not serious and usually resolves on its on. See your physician if symptoms persist or worsen or if there is fever, cough, wheeze, breathlessness.