Hi TexRex ~ Gosh, I'm sorry you're having such pain. I can totally relate.
When is the last time you had an MRI?? If it's been more than a year, it's time for another one, with and without contrast material. There could be some changes in your spine since your last one. Ask your doc to order one.
Something else --- "the domino effect." This happens when you have spinal surgery -- the levels above/below the surgery site will fail -- causing more pain & very often requiring more surgery. It happens because the other levels in the spine have to take on more of the load after fusion.
If you've had an MRI and it doesn't show anything, have they considered scar tissue? I have a bunch of scar tissue on the L5 nerve root -- most of my MRI''s show this -- but the last 2 MRI's that I've had made NO MENTION of scar tissue -- so either the radiologist didn't see it, or somehow it's disappeared -- which is highly unlikely. LOL
I'm sure you know that sitting & standing are the WORST things a spine patient can do. We just CANNOT sit for prolonged periods of time. Same with standing. We either have to walk or lay down -- which most offices frown upon.

Take alot of breaks at work, i.e. just walk around the office frequently. When at home, lay down more. Try ICE too -- use it for 20 minutes every 2 hours, according to my neurosurgeon. That helps with inflammation & swelling.
If nothing works, you may want to see a pain management doctor --- he can help you keep your pain under control. Sometimes physical therapy helps too. Best of luck & God bless. Let us know how you come out. Hugs, Lee