hi, i'm 22 and have been having heart palpitations for over four months now, i've had them before but they never lasted this long, i did an echocardiogram and results were normal, i also did a holter monitor but the results aren't in yet. I was prescribed Beta blockers but they dont seem to be having any effect, i'm wondering what could be the problem with my heart, are there any other conditions which can cause this?