Severe back pain on upper left side in a man?

Too many causes. Back pain is extremely common and there are too many causes and luckily most of the time it is self limiting. If pain last longer than a week, getting worse, have neurological deficits, have fever or too much to handle seek medical attention.
Severe back pain. Anytime i hear severe, i would suggest a physician evaluate. Regarding the location, pain upper left (near shoulder blade) can suggest muscle spasm/tendinitis of shoulder, thoracic spine/disk problem, lung/heart disease, stomach/pancreas/spenic disorder. Seeing an md could help to determine the actual location and determine appropriate testing to get a diagnosis. Too little information.