Karse (my belly,bowels) in this case means “my heart.” “Inward parts,” or “kidneys” mean tender mercies. Easterners often say, “My hearts burned for them; my kidneys kindled with fire.”
All these sayings are used allegorically, signifying sorrows and bitter weeping. The kingdom of Moab was to be invaded by the king of Babylon and punished for its sins.
(Lamsa, George M. 1964. Old Testament Light. San Francisco: Harper Collins., pg 648)