I get occasional lower back pain, but I have never associated it with HRT. It started back in my 30s, with a cross-country ski wipeout. I got it chiropracted back into shape, but it can go out of whack again if I lift something carelessly.
I got a chiropractor to teach me a stretch that I could do unassisted to fix a sacroiliac dislocation, which is what I generally get. If I throw my back out, doing the stretch for a week will fix it, which is much quicker than letting it heal itself.