Good day, my 12month old son has been passing gard stools since birth. we took him to the doctor and nothing has change. what could be the cause?

Diet/retaining: Some kids have slow transit of the foods through their gut resulting in excessive drying/hard stools. Starting at 6-9 mo some actually try to retain their stool to avoid the discomfort of passing one. Either may benefit from natural looseners like prune/peach/pear juices. Others may need daily Miralax for months ( a water retaining product).