Rapid heart rate in pregnancy?

Has anyone had this? I know my heart is working harder and it's normal for it to be a bit elevated, but I've almost passed out numerous times. I'm a nurse too so I'm on my feet a lot and it's hard to have to sit every couple minutes on shift. My heart rate has consistently been 135-140+. I realize it may be elevated, but I was getting concerned about it being this high and the dizzy spells. Even when driving. I should say my heart rate pre pregnancy was 70-80. it's quite the jump.  And it only seems to be in the morning. I'm seeing my doctor about this, but I'm just curious if anyone else has experienced it.