Heart pains doctors help please?

for the last year or so i have been getting a pressure throbing sort of pain round my heart.it comes and gos i will have it at least once daily.some times my heart races really fast normally i sit down breath try to slow it down that way.but i have started to fell fainty as well for the last few weeks.i seen a doctor about the pressure pain and i went for a screening test and had my blood pressure taken.both were fine.i don't want to insult the doctors intelligence or sound like a drama queen.today i am felling fainty and not myself at all.i am 20 years old have smoked since 13.currently on anti depression tablets-mirtazapine 30mg.and have been for around 15months or so.the nurse who done the screening test said anxiety can cause this.i have ignored it for so long-scared.but obviously its got to be salted.