It could be something like acid refux or hormones or stress or even just eating too big of a meal one day. I would say keep a diary of your daily activities and see if there is a pattern. If there is great, try and work to eliminate the trigger. If not just try and learn not to sweat it. A lot of people have jumpy hearts (ectopic activity) In an otherwise healthy heart they are completely harmless. Best of luck getting a handle on yours. Take care.
My money is on hormones. Every month since I've been getting ectopics I've noticed an increase in them around the time of my period, most women on this forum have. Like Michelle said try not to fret over them. They are very common and in an otherwise healthy heart completely benign. If you read some of the other posts you will see many of us have this same issue. Hang in there and feel better!