Hey everybody, I hope somebody can give me a wee but of advice...

I am 20 weeks pregnant! Woop woop but I have been goin through a rough time the last few weeks, I have been really dizzy constantly and black out at least 3 times a week, I can't even go to the shop for some milk without passing out and really blurry vision, nauseous on top of that. I was in hospital last week with awful pains and the dizziness and the docs couldn't see anything seriously wrong, I have been out of work for 3 weeks cus I just can't stand for long periods. They found that my placenta is still lying too low and my blood pressure is very low but they said its nothing to worry about??? Also pre eclampsia runs in my family, my mummy almost died giving birth to me and brother... Can anyone please give me some advice or has this happened to you and found out what it was? Thank yooou