Why would u hurt in ur back at lower shoulder blade, it feels like a pin or a knife sticking me in that spot?

A few things : A few thing can cause this. Zoster in its early stages can do this before seeing shingles. A pleuro-pulmonary process, nerve pain from the intercostal nerves may as well. Muscular etiology less likely. A "pinched" nerve in the lower part of the neck or the upper back quite commonly manifests this way. Start by seeing your doctor for an exam and x-rays.