I have anemia really bad I get my blood checked every three months.
Anyways in a pregnancy you can end up fainting more (passing out)/feeling weak to your legs where you need to grasp on to something or sometimes it just makes you feel kinda of fluish.
Iron does constipate you so you take it with food to digest it easier I take ferrous sulfate(just a pretty word for iron) buy it over the counter and its safe to take depends on mg amount you may have to take two talk to the pharmacist bout it.
Another thing increase you intake with greens(brocoli) greens usually have alot fibre/iron and usually wont constipate you if you take them together!!