Is there an exercise to strengthen the muscles that would keep my sacrum, tailbone and pelvic bone in place?

Try to perform this simple stabilizing exercise to strengthen this region.

Begin on your stomach on a soft surface. Place a small pillow or towel roll under your pelvis to take pressure off your back. Relax your head to one side. Raise both legs upward while keeping your knees locked and your feet turned inward. Raise your legs until you feel your glutes engage. You should feel the muscles in your lower back during this exercise. Pause at the end range of motion, slowly lower the legs and repeat. Perform two sets of 10 repetitions.