Everyone is a bit different, so I can only speak to my experience. Mine was due to car wreck and included a broken femur with rod and pins and some other party favors. I now have a piece of rib and a steel cage with what I lovingly refer to as deck screws in my back.
I am blessed to get around very well now and actually lift 40-50 lbs bags at times, but in a VERY methodical manner. I've learned my limits albeit they're not as bad as I thought they would be nine years ago. That took time.
As I started writing this I saw I was likely just repeating the things your doc and physical therapists have told you. Basically have patience, be a good patient and things should get better. Yes, it starts slow. My first day after surgery (with help of two men) was back brace on, stand up, one step, sit down, lay back down and rest. On day two I sat in a chair for 30 minutes.
Here's the visual I have for this:
If you can imagine taping a small pipe to the middle of a fishing rod, that's your back now. The middle part doesn't bend, so the areas above and below the pipe will get much more stress when bending/lifting/twisting.
Some suggestions:
Take Care
Thanks..... I hope to be as well 9 years from now