My iron was VERY low when I was last pg. My ND put me on Carlson's chewable Iron. I only needed to take one 25 mg per day and my iron levels were much inproved in a short time with no constipation, no stomach probs,etc. and the fatigue was greatly reduced after only a few days. My MD was going to have me on like 250 per day!
I did not take Floradix as I didn't know about it then. But I have given my 17 mo 2 lg. bottles total of Floradix (over about 3-4 months time) and he doesn't seem to have any problems with it, but I only give him small doses. I hope you aren't allergic to something in it.
Maybe you need to start with a half dose then work your way up by adding another 1/4 dose every couple of days? Or maybe, especially if your due date is close, you can tolerate it while your body adjusts to it?