Well that SI joint issue stinks. Can you swim or float in water? My friend had some sort of SI joint pain and doing that ultimately gave her a lot of relief. Physical therapy can't help? My merve extremities tingle and I have been given "nerve flossing" exercises. I am no doctor so I say this for encouragement, you may be able to do some exercises/ strength training at a very low level. I have had to dial back my weights due to bursitis but I still use resistance bands and low weights like one or two pounds. I do push ups with a heavy band around my trunk to support most of my body weight. This is to say, if you can find the right program, there may be ways to adapt exercise to your issues. Or maybe tai chi or yoga may help with the joint/nerve pain. As for walking, some people claim that using a weighted vest helps to build bone strength. If this is irritating chatter because you have explored everything umpteen times, my apologies! I do wish you well in figuring out how to best meet your challenges.