There is a great deal of information about golfing technique available to all who play this great game. Professionals and amateurs alike diligently work to improve their games by making adjustments to their swings. To avoid too much body movement and losing posture often they will try to keep their pelvis stable by trying to point their belt buckle to the ground at address. Many find this extremely helpful with their swings while others find it creates a problem.
Most people in general, golfers in particular, are known to have tight hip flexors (muscles in front of their hips). Tight hip flexors will cause the pelvis to tilt forward causing your lower back to arch. Pointing your belt buckle to the ground will increase the arch in your lower back. This increased lordosis puts enhanced compression on your lumbar facet joints. Over time the joints can inflame and result in lower back pain. Exercises to help you adapt to this new body position include pelvic tilts and knee to chest stretching as well as foam rolling your hip flexors.
However if you continue to notice your lower back getting tight, stiff or feel some lower back pain it would be helpful to be seen by a sports medicine specialist who specializes in golf. They will diagnose why your symptoms are occurring and set up a treatment regime to alleviate your symptoms and enable you become more stable with your golf swing. Do not get frustrated and question your ability to golf. See someone that can help you and continue to enjoy the great game of golf!