It is normal because you are sharing blood with your baby. My doctor explained it to me. I still get dizzy and I'm 35 weeks along. Just take things slow, drink plenty of water and eat right.Don't try to over do anything and make sure you tell your doctor. They will want to check your blood pressure to make sure it's where it need to be.
Make sure you're drinking LOTS of water, if it persists after that make sure you tell your OB!