The answer is two fold. A big reason is because you are starting to build your blood supply now. You will have almost double the blood volume as you did prior to getting pregnant (by the third trimester or so). Right now the progesterone that your body has been producing has relaxed the joints in your body, and has relaxed the blood vessels to make room for the added volume of blood about to be produced. Many women feel quite faint right around 15 to 17 weeks as they haven't really started to add to blood volume yet, but their vessles have relaxed. They have very low blood pressure and it causes dizziness and fainting spells if movement is too quick.
The second reason is because you are building amniotic fluid, and you are filtering it as well. (Along with filtering your own body.)
If you start having headaches, or feel blah drink a ton of water. You should feel a lot better in 10 mins or so.
Linear Mode
