What Causes Severe Pain In Lower Ribs?

I have pain when I move on left of lower chest at waist level of my back, when I turn to left or right or lie on right or left side,but can perform all normal daily duties. No pain when I sleep on my back. Very tender to touch in space below last left rib. Cant bear any pressure round left side waist when lying down but only in that spot. It came gradually a few months ago, got excruciating while rolling onto my back one morning in bed. I was bedridden for 2 days with the pain as it was agony to move . Felt like lots of sharp ripping sort of pain.Has gradually improved but seems to flare up and receed. Never been as bad as that 2 day episode. Cant seem to get rid of it. I take strong ibuprofen when its bad.