It appears that a lot of your heart palpitations are due to anxiety, anxiety is the culprit for a lot of folks that experience them, myself included. Lack of sleep can cause them as well. The fact that your test came back normal is a good sign.
I would try not to worry, this can make them worse, try to relax, easier said then done, I know, and if they STILL bother you, then ask your doctor's opinion.
I also wanted to add that I have a history of anxiety, hense the reason for me taking the zoloft. I am a 26y/o female with normal blood pressure and pulse, and weight 132lbs.