Ive had this exact problem. i had it all throughout my pregnancy with DD and ive had it so far through this one too. my doc told me some women have bad dizziness as a pregnancy side effect for them. but she told me to make sure i drank plenty of fluids and to rest enough. and to always sit down when i start feeling that way. my sugar is fine and iron checks out so its never been the problem. dont really know what causes it but i get spells almost EVERY time i go out, expecially if ive been in a store on my feet for a little while. its scary!