I suggest you see another cardiologist. I have similar symtoms and he gave me a ekg,eco-cardiogram and complete blood work. I also had to wear a monitor for two weeks. I am awaiting my results. The ekg and eco were fine. Waiting on the bloodwork and monitor.
Good Luck
Sorry to see you have not gotten any helpful responses.
My simple view is one should always seek further medical advice when symptoms change, especially if that change is worse, not better conditions.
Also, if you doubt you doctor's diagnosis, I'd suggest trying to get a different doctor to take a look.
I simple EKG is not what I'd call a through examination of your problem. If the ectopic beats did not occur during the short period of the EKG run, then nothing was observed, and you looked just fine, you need to be monitored when the problem rhythm is present, e.g., a 24 hour or longer monitor... that's how I see it.
Good luck, it is very unlikely that your condition is dangerous, you have time to get it diagnosed and treated if needed.