I take 700 mg of iron a day why is my iron still low !?? Could it hurt my baby

ash

I’m 34 weeks and I’ve always had low iron my over the counter supplements werent high dosage enough so my dr prescribed me 700 mg in the morning on an empty stomach and I can’t eat or lay down for an hour after I take it and I take it with a glass of orange juice all in effort to get the max absorption possible, why is my iron still low? Its been about 3 weeks since I started taking it, could low iron negatively effect my baby ? Talking to my doctor is kind of useless bc she acts like she doesn’t believe im taking it bc it’s so low but I’m taking it every day