I have painful hard lump below my rib cage on the left. what could this be?

Bone spur: The usual cause of superficial lump is lypoma. Rarely could it be a small bony growth or neuroma. A lypoma is usually painless, freely mobile, and remains stable over time. Bone spur is hard, fixed and tender on palpation. Neuroma may or may not painful but usually fixed. Just monitor for changes in size, superficial ulceration, changes in color and any suspicious changes talk to your PCP.