Hi Dear,
Welcome to HCM.
Understanding your concern. As per your query you are having symptoms of  
constipation and dark colored stools which could be due to many reasons such as 
- eating a lot of dairy products
- irritable bowel syndrome
- some medications like antidepressants
- acidity
- certain conditions like 
hypothyroidism. 
Need not to worry. I would suggest you to 
consult gastroenterologist for proper examination. Doctor may order 
colonoscopy or other tests to look for blockages in your colon , barium studies and 
blood test for hormonal changes. Doctor may prescribe fiber supplement psyllium, calcium polycarbophil , osmotic laxatives , stool softeners and medicine to reduce acidity. You should start with drinking a lot of water , do light exercises and avoid fatty and heavy meals.
Hope your concern has been resolved.
Get Well Soon.
Best Wishes,
Dr. Harry Maheshwari