[Arrectiff]

Good you've hung in there and especially despite intermittent back pain. I found if I keep my waist wedged up (kinda curved out) against the stiff part of the hakama - some people even put a flat, wooden piece between back of the hakama and their backbone - I don't get back pain. Also, a long soak in a hot bath after practice.
When out of bogu for a while, due to knee problems (from Iaido but kung-fu caused some time ago), as soon as I got all gear on, the doh seemed so heavy and I arched my back (inwards)=backache. As you know, Kendo is a "do" or Way, there for us for a long time, so continue to hang in there.