Talk to Pediatrician on Stool Issue

my son 6 yrs old often passes stool in his pants.. no constipation issue when i scold him he go to the washrum n pass stool easily .. smell of poo is also very very bad.. soil his pants 2 3 times a day with poop... but for pee he always go to washrum.. also he has habbit of eating his nails shirt button n threads.. i have found threads in hi stool many times.. plx tell which doc i should consult? he says mjhe pta nai lgta kb nikal jati h poti meri.. m much worried plx help