I fell from a ladder. i have a mild pain on my left side below the ribs . it hurts when i stretch to my right side . what could it be ?

Pain: You probably strained some muscles in that area. Take some Aleve (naproxen) twice a day, heat to the area. It should get better in the next 5-7 days. If pain gets worse (any abdominal pain, nausea/vomiting) then see a doc.

Bruise: Its probably a bruise within the muscle. Especially since it hurts to stretch. (But the spleen also lives below your ribs on the left. The very worst thing that this could be is bleeding in, or from, the spleen.)