The iron tablets I am on are in a green and white bottle and they are little red ones. i take one each morning with my other tablets (vitamins and calcium). I was expecting constipation but I go more regularly now than I did before taking, but doubt that has anything to do with the tablets. Probably the pressure I am getting now doing that.
You can get a stool softner from chemist that is safe during pregnancy rather than a laxative that can be too aggressive and cause cramping.