Pain in rib area?

So this might sound weird but for the past few years I've noticed a killer pain in my left (lower) rib cage area after sitting too long.
This only affects me when I sit for extended amounts of time (desk/driving/etc.)
I have a short torso and I'm wondering if my excess belly weight smashes my rib cage when I sit and that's what causes the pain?
I know that sounds ridiculous but it's getting harder for me to sit down for any amount of time now. :grumble:

Anyone else have this problem? I'm 5'9 and bouncing between 153-156 lbs.