Heart palpitations?

Does anyone have these? 
I've noticed they happen more when I drink a lot of caffeine but not always. Or when I am stressed. Lately they have been getting stronger to the point I feel very faint and almost like I'm going to black out. I am a VERY anxious person who has a lot of anxiety issues so maybe that's part of it?
The doctor didn't seem too worried but when he feel faint and almost pass out, I think that maybe a problem?!
Should I see another doctor??
I'm 27, not overweight and fairly healthy and have been getting them for over 10 years.