Pain near lower ribs. If it is serious?

Hello, From past few months i have discovered pain near my lower end of ribs..it actually feels inside of lower portion of ribs, image 1. During day i feel completely fine but it tends to increase if I stretch or lay down for more than an hour or so. Usually while i sleep it gets so sever that I can't sleep with straight back and tend to ease if i turn and put a pillow or something near my stomach for support. Also while lying down in straight back position i do get pain when I exhales completely and at this time its inside of the area where ribs connects near chest, image 2 This never happened me in past and recently I shifted and The matress on which I sleep don't feel premium and feels it could be because of that as well as it never happened in past. Also if I sleep on the ground on cotton matress it feels it eases pain. Could someone throw some light whats going on and if it is serious??