What Causes Swelling Below Left Rib?

Hi, I'm 36, active female, great health generally but have had a bump/swelling like area along my left lowest rib. It's never painful and if I press it, it flattens as if it's tissue. It's always been there since I can remember but when I put on weight, it gets bigger too. 2 years ago my doctor told me it was just the shape of my ribs. Can you have fatty tissue there?