Prenatals with low Iron?

Im in need of some serious help. Before I got pregnant I alway struggled with being able to use the bathroom. Even when I was pregnant with my son I had constipation but it went away after a while. But now! Im dying having been constipated for over 2 weeks and I think its alltuhe iron from my diet and the prenatals. I've tried looking online for prenatals with low iron but nothing specific comes up so I was wondering if any of you ladies have found anything? or have anything to recommend?