Your back pain is likely caused by the sacroiliac (SI) joint, and your pelvis is generally misaligned. I’ve suffered from this issue for at least 20 years, since I was a young boy. Two months ago, I finally found a "specialist" who noticed I was walking a few millimeters off. He straightened me out. The problem returned quickly, within days. But now, by doing glute walking (lifting all other limbs, including legs, and "walking" forward slowly on your glutes, like you would with your feet), I’ve found relief. Another trick to possibly realign the SI joint at home: lie down or sit, place a pillow between your knees, and squeeze as hard as you can. (Of course, I can’t recommend this since you’re preparing for surgery.) If you hear or feel a click in your lower back, the SI joint likely popped back into place.
The problem is that if your pelvis and SI joint have been misaligned for a long time, your spine is likely misaligned all the way up to the base of your skull. So, the entire body needs to be realigned. I recommend an experienced manual therapist. Unfortunately, there are differences among these specialists, so the first one may not fully resolve your issue.
Haha, just noticed now—your lower back pain is already gone! 
