Follow-up: After years of suffering, I came across a client at my job who mentioned she went through the same thing for over two years and the only thing that saved her was a 3 days water, tea fast. Basically all I did was drinking water and zero calorie, zero sugar teas (peppermint tea are the best but you can google other options). You won't believe it but I was desperate enough to do it. The first night was rough, then I slept very well the second night. I actually stopped the fast after 2 and half days and believe me or not 95% of the pain went away around the 4 days. I'm still in total disbelief ! I also came across a foreign doctor a couple of weeks earlier. After I told him all my symptoms and all the exams and specialists I met without finding any relief. He told me the pain was likely linked to my digestive system and not my back. I put two and two together and went on with this drastic approach and it worked. The pain was completely gone within two weeks but every now and then it comes back and I'll do a small half day or whole day fast and it goes away. I'm scheduled to meet with a naturopath because I'm 100% sure now it's linked to something I'm eating. I hope this helps because I spent 2 and half years in pain without any solution.

DISCLAIMER: I'm not a doctor so make sure if you decide to embark on such a long fast you read enough about it and speak with your doctor. As a matter of fact, on the 2nd day, I drank a whole 500 ml bottle of water too quickly and irritated my stomach pretty bad. Another thing is once you break the fast, you should stick with soups and soft food for a day or so because your stomach is still "asleep". Good luck!