Many women start to feel this symptom within a week or two after pregnancy has occurred. This one is pretty obvious. When pregnant your body is going through some major hormonal changes. Your temperature is also higher due to the amount progesterone circulating through your body which will also make you feel a little sluggish. It usually happens around the same time you would have gotten your menstrual period.
Some women assume they have started their period when in fact they are pregnant.
The spotting is caused from implantation which is when the fertilized egg burrows into the endometrial lining. The growing uterus compresses major arteries in your legs which causes your blood pressure to drop making you extremely light headed. Skipping meals or going too long without eating may cause you to feel dizzy or faint. When not eating frequently enough it causes low blood sugar. Blood sugar is the primary source of food for your baby so it will be depleted much more quickly.