Health concern] How can I improve my lower back pain?

Recently, my lower back pain has been getting worse.

Since I sit all day, it's naturally difficult to maintain good posture at every moment. Sometimes, I even have to return from a walk because my back hurts too much. I try to do exercises and stretches that are supposed to be good for my back, and I avoid bending movements. The hospital's physical therapy also doesn't seem effective given the current situation. Since the pain isn't constant...