How long do babys go thru withdrawal?

My son was born addicted to drugs. I honestly don't know what all drugs she used, but it was alot. She has never told me exactly what or how much, but her mom told me it was everything and anything she could get her hands on. Ds went through withdrawl for about 6 weeks. His main symptom was grunting. He grunted like he was in pain most of the time those first weeks. He didn't sleep well at all. He even grunted in his sleep. It was so sad. So senseless. Today he is a vibrant, smart, rowdy almost 22 month old who seems to have no lasting effects from his exposure. He does have some digestion issues that concern me. He has loose stools very often. He is not in pain from it and it doesn't seem to bother him. His Pedi said it may be from lacotose intolerance. We have been lactose free for a week now. I've seen some improvement, but not much. Oh and ds's bmom is my dh's cousin! Will your adoption be open? We don't have much contact with ds's bmom due to her lifestyle, but our adoption is open.