What Causes Heart Palpitations?

hi, im a 20 y old male, 5 foot ten weighing around 11 and a half stone, do endurance weight training a couple of times a week as well as playing amatuer football, been suffering from heart palpatations for around eight month now,a dull ache in the back around the heart area and i seem to be constantly lethargic and tired, ive been to a local walk in centre for an ecg, doctor claimed this would be solely down to my diet..ie skipping breakfast, i've been ensuring i get my 3 good meals a day and it doesnt seem to be making any difference and if anything the sypmtoms are getting worse! i do however smoke ten cigarettes a day, could this be a large factor? is there anything you could advise? obviously this is having a big impact on my life and im starting to worry, thanks, alan