How do I know if I'm having side effects?

Ok- I have been having heart palpitations for a couple weeks; last week I started also having chest pains. I went to the ER, got admitted overnight, bloodwork, ekg, stress test with echocardiogram, all pretty much normal, and they sent me home with a Holter monitor. So, with all the serious cardiac stuff ruled out, now they are looking at gastric reflux as a cause for the chest pain, at least. I got my prescription filled and was reading the printout about it- in the ‘contact your doctor immediately’ portion, it lists chest pain and irregular heartbeat. Since I’m already having both of those, how on earth do I tell if it’s because of the medication?