My Grandson Of 31 Months Is Well On The Way

my grandson of 31 months is well on the way to being potty trained and never wets his pants but when he says he needs a poo will only wee. he complains that his bum is sore and will pass a small amount of soft stool but soon again will need to poo and so the cycle continues. he eats well, porridge fruit veg including beetroot, wheaten bread etc but i am worried that he may have a blockage or other disorder