my son had a surgery  8 month ago ( a bowel pull through surgery for his recatal mass) at age  of 8 month . and i have been changing his diaper at least 10 times a day but no bowel movement at night....i have been to his surgon(stated he is not incontinant) ,peds, and gastroentrologist with no help(they said all his stool test was negative). he always has a diaper rash....i dont know what to do next.