I'm so sorry you are in this fix. I suffered from back pain for many years and I know how limiting it can be. I am lucky to live in a country with alternative forms of medicine. I took an aryuvedic treatment which uses plants and other natural ingredients for massage oils and tonics. I took a massage treatment with oils for two weeks and my pain has been gone for the most part for some years. Maybe there is some form of alternative medicine available to you. Yoga can help, homeopathy has good remedies with no side effects and acupuncture might help.
I hope you are able to continue gardening. I understand that it is very important to you.
Good luck.