Miralax, (called Restoralax or Lax-a-day in Canada) is an " osmotic" laxative (believe Milk of Magnesia falls into this category as well). Recently, Miralax stopped being effective and caused unpleasant side effects. Until I see the gastroenterologist in two weeks, I have started taking Senokot (a stimulant laxative) and magnesium supplements.
I also find it sometimes helps to start the day with two mugs of hot water with lemon slices.