Welcome to Neuro Talk. There are alot of folks here that have back issues. I hope more will chime in. Have you gotten multipal opinions about your DDD?
In some ways, I understand what you doctor said about not doing more surgery for fear of making it worse. That is why going for multipal opinions is good. There is something called the domino effect, where the ones above your fusion and below it fail, leading to more fusions. That is a rut you don't want to get into for sure. I have had two fusions. No more for this gal....
PT gets to a point where it just doesn't work. Have you tried acue puncture?
Ketamine infusions? The other ones you mentioned didn't help me either. There will be support here, no matter what you face. Welcome again to this site, and feel free to explore the forums. There is alot of compassion here. ginnie