I have been having lower back pain for a long time now. what kind of doctor should i seek to get a "scan" and a diagnosis so i know for certain whats going on here?

One of the most common things primary care physicians see and treat is lower back pain. I would start there, and they can refer you for any appropriate tests or consults with specialists.

Would start with primary care, and depending on exam, a physiatrist might be next. Assuming no neurological findings, would recommend physical therapy and learning McKenzie Back Exercises. If overweight, would recommend dietary measures (such as DASH diet). Imaging is not necessarily of value in many cases of chronic low back pain. Would attempt to localize pain generator clinically.