Do I see a regular doctor for back pain first?

Yes. Yes, you should see your regular doctor first. There are a lot of causes of back pain. Your regular doctor should be able to manage majority of them and if your pmd can;t, he/she would be able to refer you to the right doctor/specialist.
See pain specialist. Your general practioneer has very little to offer for treatment of back pain other than meds, pt and time. They also tend to refer you for surgery as a fist response. If you pain is severe, i recommend a pain specialist who can accurately diagnose and treat the underlying cause of the problem. If you need surgery, he/she will recommend one for you.