Horrible pain in upper left shoulder, numbness of left arm, mild upper chest pain. also short of breath. what is it?

Several things: The most important thing you need to rule out asap is a cardiac problem. Other things could be inflammation of the pancreas, a musculo-skeletal problem or upper abdominal organ problems. Regardless, you should be checked right away.

See your Doctor: Must have complete evaluation. If sudden you may need emergency medical intervention or you may not. You must see your phisician asap and obtain a diagnosis.