I also have recurring pain in my back, centralized in the middle of the small of my back.
The abdominal pain
seems to radiate from my lower left side
(more toward my belly button rather than the side, about even with my nipple), and comes and goes, with sharp pains once in a while. If I press on the area, there isn't any tenderness. If I try to sleep on my right side, it hurts, but if I lie on my back or left side, the pain goes away.