Sorry OP I was posting while breastfeeding.
When you are pregnant your iron levels - haemoglobin - are lower and the lab adjusts the range to reflect you are pregnant.
The standard advice is to eat iron rich foods e.g. red meat, lentils, green veg and avoid eating foods/drinking drinks containing tannins e.g. coffee and calcium e.g. milk that inhibit iron absorption. Red meat has iron in a form that is more easily absorbed by humans than vegetable sources.
If you then are found to be iron deficient you need iron tablets that contain far more than the RDA for pregnant women and you need to take 2-4 per day depending on the doctors advice. These are tablets such as ferrous fumerate, ferrous sulphate or ferrous gluconate which contain something like 60mg of elemental iron per tablet. You can buy these at a pharmacy at the discretion of the pharmacist but being pregnant you most likely need a prescription.
Ideally iron tablets should be taken on an empty stomach e.g. hour before food or two hours after with vitamin C to increase absorption. However if you have horrid side effects like bowel issues then taking one dose before bed may help over come this. (And yes your poo will be black.)
As someone who is frequently iron deficient I don't advise you to drink loads of juice with your iron tablet due to the high sugar content. Have a small amount or take a vitamin C tablet instead.
In my case my hair always starts falling out when I'm iron deficient.