Constipation

I have had low iron and basically struggled with on and off anemia my whole life. Throughout this pregnancy my blood work came back for extremely low iron. I am being treated for anemia. I am 29 weeks and 5 days and the iron pills have me really constipated. I tried extra fluids, prune juice, dates, cranberry juice, apple juice and apple sauce. Nothing seems to work, my doctors office is closed till Monday and I have been straining trying to use the bathroom. What is something safe that I can take during pregnancy to help me?