I have intermittent intense burning pain just below the left side of my ribs. I get this mostly w/ sitting and feel better w/ stretching or lying down. Sometimes I can feel a muscle spasm and it is tender to the touch.?

Abdominal pain L. Many causes— pancreas, kidney stones, bowel disease— you may want to go to urgent care to get some blood work and check up. Hydrate as best as you can .
Sprain? You might have sprained your rib cage by limiting something heavy, straining, or assuming an unusual posture. However a rib fracture cannot be ruled out. If this pain is not relieved with cold/hot pack and NSAID after 2 weeks or gets worse, consult your family doctor.