Most of the day? If you have a disc issue sitting all day is probably not helping making things feel better. Or even sitting a majority of the day.
I don't think you've had all the tests done that would rule out a disc problem or rule out a specific problem though you mentioned an MRI which can pick up plenty but not always everything and also sometimes things feel worse than they look on the MRI.
If you have the MRI report can you tell us what it says? If you don't have it you probably should get your copy of reports, scans and such for your own personal copy anyway.
Can you find another spine doctor to go to? If it's not a Worker's Comp case then you should be free to look for someone that you want to go to unless you've got an HMO type of health care plan.
You said you had selective nerve root blocks and I'm wondering if you've had lumbar epidural steroid injections?
Here's a great website to go to and get informed/educated and it would be helpful to you I'm sure. It has been greatly so to me and many others:
ChiroGeek's Home Page
Back/spine pain is depressing no doubt about that especially when it's significant to interfere with one's life/lifestyle.
Please keep us posted and hope we can be somewhat helpful to you. mmglobal (Mark) would be a really good person for you to talk to. The spine journey can be such a maze. Continued good thoughts~ Maria