Get back X Rays or an MRI so you can see what's really going on!

Not sure what your bf% is but lowering bodyweight in general will put less strain on your back. Also, could be that you are stronger than your skeleton and joints can handle. There are many ways to build muscle, but perhaps you need to lighten your weights a bit, build some muscle in those sensitive areas, and go from there.

Additionally, you should see a doctor about this. The back is an area with lots muscle, however it also contains your spinal cord, and an injury in this area could really fuck you up for a long time. Nothing is as debilitating as a back injury. Seriously, even just a pinched nerve or slipped disc fucks me up for at minimum a week. You dont want this problem to become a bigger problem!

Sounds like you may be lifting weight that’s too heavy for you and you’re compromising your form to get your reps out. But that’s a vague question. You might also have a herniated disk.

Could be a lower back pump

What is causing the pain?

Hips out of alignment, core and glutes are weak causing pelvic tilt, maybe carrying around extra weight(too much fat and water)

would like to hear answer too, I have the same problem, I stopped doing heavy weights and pain is slowly going away, but this is not a solution