A normal non pregnant woman would have an average iron count of 12, iron helps to increase red blood cells, these in turn carry oxygen around the body effectively.
A pregnant woman has an increase in their circulatory volume as they are taking on a baby too, and so the blood becomes diluted. In pregnancy your iron count can drop to 10 or even lower depending on you and there is not enough red blood cells available to carry oxygen around - causing tiredness, low blood pressure and fainting.
Feeling hot in pregnancy is normal too as your circulation to your skin has increased from hormonal changes in your body. This can leave you feeling hot and sweaty, wearing loose clothing, natural fibres such as cotton, washing frequently and keeping your room cool with a fan may help.
http://hubpages.com/health/Minor-disorders-in-pregnancy
