Are Rapid Heartbeats For A Few Seconds Normal?

I am 32 years old and for the last two years I have had strange random heart palpatations. I have had multiple EKGs, stress tests, blood tests etc. Other than a few low results from iron and vitamins B and D everything has been normal. I am over weight and have diabetes, however my diabetes is extremely well controlled (my a1c is 5.3) and my cholesterol and blood pressure is good and my triglycerides are great. Because they couldn't find anything they said it must be anxiety, even though the episodes only last mere seconds and I am fine until the next time it happens which could be hours, days, or weeks away. Lately I have had a new "sensation" of what feels like vibrating actually in the upper section of my left breast but with no pain. last night it was so intense it actually scared me. My doctor already thinks I am a hypochondriac and each time I go in with these syptoms I am told it is just anxiety...so do I ignore it or not?