I suffer badly from sacroiliac joint pain. i can't manage walking for more than a few steps. the problem has become progressively worse over 11 years. i've already tried a belt and physiotherapy

Could be an illness.: Lower back pain is one of the most frequent problems that all of us may experience at some time. The sacroiliac pain may however reflect a systemic illness like arthritis or autoimmune disease. It sounds like local treatments have not been successful thus far. I believe you will need an x-ray, if not already done and suggest a visit with a rheumatologist, to help obtain more targeted care.