I have sciatica as well due to degenerative disks, stenosis and possibly my osteoarthritis from back injuries while in the military. I dive mainly shore dives so I went to side mount early and tend to tank up at the water edge or in water with LP50s. When it's really bad I just don't dive. Being in the water I find very helpful as I'm weightless so I'm now looking at a wagon to haul my gear to the water if needed.
One of the collapsible canvas carts will work well for you. That's what I use. Just search for "collapsible wagon" online.