You to discuss this with your doctor to make sure everything is in order.
I would speak to your OB. It could be because of the increase in blood volume or low or high blood sugar or dehydration. If it bothers you than don't do it ;) seriously though I would ask your OB what's going on. Make sure you are eating meals frequently and mixing carbs with protein and of course getting enough liquids. Stand up slowly and if you start to feel that way sit down. Feel better!