What Causes Pain In Ribs While Sitting?

Hi, I m Michael from Australia... I have put on weight (12months after quitting cigs) when I sit on the lounge, it feels like I lean too heavily and now my ribs ache sometimes. When I stand or move it eases. Is it because I m heavier? Im 6ft1 and always use to be 105kilos now I m 118 lol sigh.