sounds like you have been thru alot already. Ditto on the injections. Inversion is nice, but there are decompression set ups availible that work IMO alot better. I bought a neck one on ebay for cheap (a professional rig like th one the doctor rented me at PT). Since I knew how to use it, I could use it more frequently than the 3 times a week i was going to therapy. Very helpful. Also, lose the gut and get into an excercise program that works your back (walking ferqunetly short distances maybe to start) is really helpful.
Good luck. If you need to chat drop me a pm and I can try to help. These back problems become debilitating and ruin your joy in all the things you "use" to do. You gotta adapt and still move forward and do stuff that you DO enjoy, maybe modified (I have switched from racing Motocross to boating for example) and still do mild trail rides, but the days of full on 6 motos is over officially for me. I still do special events and like to go out to the track with some buddies for fun practice at the track ,but I dont do doubles and I pull off BEFORE my back starts to feel tweaked.
Good luck.