I'm 34 weeks and I have the same symptoms, along with my feet swelling and heart palpitations (feels like I've just run around the block and I haven't done anything). My blood pressure is steady at around 110/65-120/80 range, so nothing to worry about there, so they sent me to get an ultrasound done of my heart and I had 2 ECG's as well. The conclusion they have come to is that I'm stressed (tho I'm not HUGELY stressed) and I have a heart murmur that's just not always coping properly with the 30% more blood in my system from being pregnant. And the fact all my organs are squished etc etc (normal pregnancy stuff).

I'm already on bed rest for the rest of the pregnancy (have been since 23 weeks due to nasty hernia needing surgery), so they are just telling me to continue to rest as much as possible. (which is completely possible with 3 kids, particularly a 15 month old. Not. )

Good luck with it, tho! Hope it's nothing to worry about.