I Do Not Know What Triggers It, But From Time

I do not know what triggers it, but from time to time I suffer from a tenderness of the skin and pains rather like a hard pinch around and at bottom of the rib cage... never at my back. The tenderness of the skin and the pains seem to occur at random but are severe enough to deny restful sleep. This episode is occurring as I battle a bad case of the flu. I seem to have had these episodes as long as I can remember... my doctors... so far... have no idea.