Hi... Welcome to healthcare magic. As you mentioned you have problem of lactose intolerant that can lead to diarrhea not constipation. If you have problem of lactose intolerance than avoid dairy product and milk. Lack of high fiber foods and lack of water intake in diet also cause constipation problem. Lack of gastric motility or intestinal obstruction or other reasons may lead to constipation problem. Bulk forming agent like psyllium is helpful in constipation. Take a high fiber foods and water intake in diet. Avoid too fatty foods and junk foods. Consult a gastroenterologist for further diagnosis and treatment. I hope this will help you. Get well soon.. Thank you.