Pain in lower back on left side above buttocks when sleeping at night, i lie on my left side...in the morning i have a very tender area just above my left buttocks and below my rib cage.

You : You may be straining your back muscles or facet joints. I would recommend alternating with your right side and sleeping on your back. You may also benefit from trying out a different mattress. If it does not improve or worsens i recommend discussing it with your primary care doctor. Good luck!

Many : Many people complain of back pain. Pain in the area you are describing is more consistent with muscle pain than with nerve pain (often referred to as a pinched nerve). The main things to consider is good shoes designed for your specific activity level, sleeping on your back instead of your side, and stretching regularly during the day and before going to bed. If the pain worsens or does not go away, i would recommend a full evaluation.