well it can simply be an anxiety/stress issues..
proper history and examination required...
If possible please visit Fatima memorial hospital shadman lahore Cardiology department and meet DR ZARRAR ARIF BUTT with marham refrence
I will suggest Thyroid Profile (FreeT4, TSH) to rule out your palpitation , if your ECG is normal(as you mentioned).
Get this test from INMOL hospital Lahore or from any reputable lab for good results.