I have had the same throughout, not running to the loo, but certainly much looser than usual. When i was taking iron, WOOOHOOO did that get explosive?! And for most people it causes constipation. ( Out of interest, my mum reacts to iron in the same way as me.)
Like people have said, the hormones can act in different ways for different people. The bonus is that you are less likely to suffer from 'roids' or fissures with loose stools!