Hi and welcome,
if your doctor listened to your heart and examined you and was reassured that everything was ok, then maybe you might want to ask him why you are feeling the chest tightness. and maybe for a mild anti anxiety agent. if he/she does not - then I would perhaps check out a cardiologist. you might have a pinched nerve, or something.
at 24, you are very young, and try not to worry. this is a good forum, many wise people here with experience and dedication. best to you.