Pulsating pain in heart

Im a 15 yo boy and for the last 3 days I've been having discomfort in my left side of chest/ Heart area. It worsens with my position eg. Standing up or bad posture. It feels like i have a stich in that area and im quite worried

I also have my GCSE exams and a GRADE 7 piano exam in 3 weeks, I am

quite nervous but its not terribly bad?

I also have my GCSE exams and a GRADE 7 piano exam in 3 weeks, I am

quite nervous but its not terribly bad?