Ay sis, that's a common side effect ng iron supplements talaga, a few of us pregnant moms experienced the same thing din, parang ang tagal ng adjustment period! The constipation and dark stools are normal, pero kung sobrang frequent na parang 2-3 times a day and feeling off ka, better check with your OB just to be sure it's not something else, kasi baka need mag-adjust ng dosage or try a different iron brand na mas gentle sa tummy mo.