I have a back injury, but nothing is on the x-ray or mri. who should i go see?

Several options: Mri and xray have ruled out bone lesion, disc herniation, spinal cord injury. This means you do not need to see a surgeon. Most likely etiology is a biomechanical issue. Prmary care sports medicine physicians, physical medicine rehabilitation physicians, chiropractors are each trained in somewhat different ways to evaluate and treat non-surgical back related conditions.