I get a sharp pain in my lower back when i stand for a long on the left side. its like a pinch...could it be a nerve?

Back pain: In most cases, a pinched nerve will cause pain that radiates into an extremity. If your pain is isolated to your back then it is unlikely to be a pinched nerve. Back pain is a nonspecific complaint which could be caused by any number of things such as degenerative disc, sprain, etc. Most back pain resolves on its own within a short period, so if your pain is persistent then see a physician.

It could be but more: Likely it is more related to a structural problem in your back in terms of load bearing across the joints of your back like facet joints or the discs or even a sacroiliac joint issue. So avoid prolonged positioning and keep in shape in terms of exercise, weight control and not smoking. If it worsens or does not improve, get evaluated by your physician.