Tachcardyia. I do now plz answer this!

Sir, i am 17 years old while I was playing my heart rate suddenly increase too fast and I quickly consult dr he adviced ecg thyroid and hb test all r right.then after few days  suddenly I feel same thing and I consult physician he consult medicine named as metpure xl 25 and anxiety medicine while taking this medicine I was fine but one day I missed the medicine and I feel again my heart rate increases and again consult he adviced ecg once ecg was right he consult medicine ciplar 40 and anxiety but while taking this medicine.I am feeling -headache daily and fatigue and if I missed medicine (ciplar40) some day I again feel same thing plz tell actually this is and what should I do now plz answer this thank you.