I'm glad to hear that the doctor is not brushing you off and taking the time to check you out!

Have you had your thyroid levels checked? I think most doctors check this when you first
go in to get the pregnancy blood test. I suffered from Hyperthyroidism with one of the symptoms being quickening of the heart when I could actualy feel my heart beating (called tachycardia) which was very unpleasant and needed medication to fix.

Just a thought that maybe you could be experiencing something similar? If the doc has not checked your thyroid levels get them to do so, a simple blood test can find out if they are 'normal' or not.

Good Luck!