I have a lot of experience in the area of lower back problems. I had a body surfing accident in 1989, and I have had back surgeries in 1989, 1993, and 2004. (each of these was a so-called disk removal surgery, with the more formal name being a partial laminectomy and micro-diskectomy).
Here are some things that I know now, that I wish I had known back in 1989:
1. Whether you have had surgery on your back or not, find a good physical therapist. Good ones are hard to find, you have to ask around a lot. I was referred to a physical therapist in 1989 after my first surgery, but that one was mediocre. The physical therapist I found in 2004 was a godsend.
2. If you are having lower back problems, you probably need to stretch your hamstrings. Do NOT use the so-called hurdler's stretch to do this, because that method will put stress on your lower back. Instead, find a bare stretch of wall, put your back and head on the floor, and wedge your butt into the "vertical corner" between the floor and wall. Your head will be on the floor, pointed away from the wall. Your legs will be along the wall, pointing up vertically at the ceiling, with your knees bent. Now try to straighten one leg at a time. Hold each leg straight for some length of time - 20 seconds, 40 seconds, or longer. Repeat. Then straighten out both knees at the same time. Hold. Repeat. Then put your legs in the spread-eagled position (with your legs still against the wall). Hold. Repeat.
If you are unable to lock your knees with your butt up against the wall, try starting with your butt 6 inches or so away from the wall.
3. There are other stretching and flexing exercises that can help you tremendously. But be wary of sit-ups and leg-lifts: if you are having lower back problems, each of these can cause stress in your lower back, and potentially make things worse. I do neither of these exercises, but do different ones (to which my good physical therapist introduced me) to try to achieve the same strengthening benefits.
Not everyone who has lower back discomfort has the same root cause. The reason I am sharing this info here is that, if you can find a good physical therapist, they can teach you to learn a set of stretching and strengthening exercises that will help you (without hurting you), and that you will be able to continue on your own, after the physical therapy sessions are over. In my opinion, this is the thing you want to do, as opposed to getting treatment from anyone who wants you to keep doing repeat visits to their office forever.