My chest hurts when i take deep breaths & when i lay down there's a sharp pain & when i bend down & my chest is beating really fast. is it just gas?

No: Those are not symptoms of gas at all! If you have access to a family doctor, please see one. If not, the school nurse (your're 16?) can get the ball rolling. Sorry we can't diagnose your problem over the internet.

Not gas : musculoskeletal pain is possible , but the pain w bending makes me consider pericarditis. Unlikely gas. Go see your regular md. Cxr and ekg might be considered.