First of all, it's really good that you're going to the doctor.
But, for a little bit of reassurance in the meantime....
How do you actually feel when the palpitations come on? Are you in pain, do you feel faint &/or breathless? Not just the giddiness that anxiety can bring on - but full on room spinning & weakness that makes you need to sit down?
If no to none of the above, then try to be reassured by that. Serious heart problems have serious symptoms. Palpitations more often than not are harmless - horrible, but harmless, particularly if there are no other symptoms.
Lots of things can cause them - hormonal imbalances, caffeine, thyroid issues. I've been getting them since I was pregnant with my DS (18 years ago) & they no longer bother me. I have noticed, though, that I get them far more frequently if I'm feeling particularly anxious about something or in the run up to my period.
So try not to panic. It's probably harmless & hopefully your doctor can reassure you.