Aiyoh, tu memang normal lah sis, especially at 31 weeks, your body is working overtime carrying extra weight and hormones are everywhere, plus your baby is getting bigger so everything jadi heavier. A few of us pregnant mums complained about this stage juga, saying we literally cannot stay awake after lunch! But if the tiredness is extreme-extreme (macam you faint easily or breathe very heavy), check with your doc just to make sure your iron levels okay, sebab sometimes pregnancy anemia boleh cause extra exhaustion.