Catching Feeling Under Left Rib-Cage? Please help, what could it be?

When i'm lying down i have been finding that i get this uncomfortable feeling of something getting caught under my left rib cage. When i breathe in, it feels like something is catching, it feels like a big twinge or something, and when i breathe out sometimes it goes away but not always. this happens everytime i breathe in and out when i am lying down. i've been searching the internet for possible causes, but i can't find anything about it so i just thought of asking on here and seeing if anyone else has any possible idea of what this could be? I'm 16 and it has been happening everytime i lie down for the past couple of months. Thanks