I can't remember if you ever used BO. I first experienced back and pelvic/hip pain for no physical exertion reason when I was using BO then it slowly tapered off. When I started estradiol it came back with a vengeance. Now after a year my rear is pretty set in place from pelvic tilt.

If I remember the explanation, the basically increased female hormones make the hips move into a position that will ready them for child bearing, that's probably an over simplification.

However, interestingly enough the shape and development of the pelvis is one way forensic anthropologists determine sex in skeletons.

So congrats, it sounds like you are experiencing pelvic tilt, a great step towards feminization. You should notice your butt starting to stick out a little bit and jeans and slacks a little tighter in the rump. One of the many reasons I switched to HRT.