What would cause my back to lock up resulting in not being to straighten it back up and extreme pain and what can i do to help it?

Multiple causes: Your back can " lock up" either due to muscle spasm or secondary to mechanical issues at the small posterior spine joints called facets. Muscle spams could also be secondary to lumbar disc disease possibly irritating a spinal nerve. A good history and physical exam by a pain specialist or a physical medicine physician should help in an initial diagnosis, to be able to formulate a rx plan.