You get a bit of your daily requirement in a multivitamin, but it's worth looking at your diet to see if you're already consuming foods that have iron. Some of them include grains, leafy green veggies, baked potatoes (4 mg.), blackstrap molasses and PIZZA! (Who'd have thunk?)
Have a look here:
Iron Rich Foods Can Fortify Your Blood - BloodBook, Blood Information for Life
I guess there are different types of iron, too. Maybe a visit to a nutritionist would be helpful.