What Causes Sensation Of Something Sliding Between Hip And Spine?

When I lay on my side, I get the sensation of something sliding around between my hip and spine. My hip hurts most of the time now. I've lost some weight, but my waist (where this sensation occurs) has not gotten any smaller. I feel sharp pain occasionally. Not alot, but more noticeable when I am stationary. This has been going on for a couple of years, but is definitely getting worse. My description is that some organ is detached and is moving around inside my lower back area. That is just a description of what it feels like.