Lower right rib pain

Hello all,
I did about 50 minutes of cardio today and about 3/4 of the way through I got a sharp pain under the bottom of my right rib cage. What gives, does anyone know what it is or what I did wrong?

I am not sure if they have officially figured out what causes this but the most up to date research thinks that it's the ligaments of the liver pulling causing the pain (or something like that). What works for me is to do some forcefull exhaling every second or third breath after it starts. It is also recommended that you alter your stride a bit until it goes away.

Thanks for responding! I was on the Arc Trainer and was going at it pretty intensly. Maybe I was leaning to one side more then the other?