Iron Supplements

I took my glucose tolerance test yesterday and the results must be in already, as there was a message on the answering machine about my bloodwork results. The doctor wants me to start taking iron supplements 2 times per day, so iron must be low. Makes sense...I have been feeling like crud by the time mid-afternoon hits. I am already taking 27 mg of iron in my daily supplement already, so how much more can I need?? I have to phone back to get the specific instructions, also they might have a different opinion if I tell them how much iron I'm taking every day already. I hope I don't have to get an iron shot in the bum, it is supposed to hurt a lot!