In cases of extremely loose stools or diarrhea that does not go away within 1 to 2 days, or blood or mucus is present, a dog should be seen by a veterinarian as soon as possible. Your dog does not seem to be suffering from severe diarrhea and seems to be otherwise functioning normally and has not lost weight, but 3 weeks is a long time to be suffering from this complaint and there is a real risk that your dog will become dehydrated and therefore suffer from secondary complications. While it is quite normal for dogs who suffer from anxiety or a change in accommodation to suffer from mild loose stools, it is unlikely that this would last for 3 weeks. I would therefore recommend that you visit your veterinarian for a thorough examination.

The most common medical causes of diarrhea in dogs are coccidiosis and giardiasis. Both of these ailments are caused by protozoan parasites that live in the intestinal tract. Most dogs become immune to coccidiosis with age, and giardiasis is normally contracted by ingesting infected food or water. Because giardiasis can block the absorption of nutriets from the intestines, it is important to have this checked for.