Trouble With Iron Supplement Pre-Op

I'm doing the pre-op diet right now and will be having surgery next Monday. The diet is going fine, but I'm having trouble taking my iron supplement. I'm taking a Centrum chewable multivitamin twice a day which has iron in it, PLUS I'm supposed to be taking a Feosol Carbonyl Iron before bed each night. The Feosol makes me seriously ill. When I take it, I get this horrible burning feeling all over my body, severe sweats, abdominal pain and cramping, and diahrrea. It's bad...it puts me in bed and close to the toilet all day. Just the diahrrea wouldn't be so bad, but the pain is pretty intense. I can't keep doing this...I'm missing work, and sitting on the toilet weeping for half the day can bring a person down pretty quickly. Can I just leave off the Feosol? Is there something else I could do instead? It's so horrible, it makes me want to cancel the surgery. Any advice? Thanks to you all! : )