Get the dog examined!

The most likely cause of the signs you describe is chronic active hepatitis; however, it could be due to something else, including a tumor. You need to have your dog examined by a veterinarian as soon as possible to determine the exact cause of the problem. It certainly is not due to tapeworms.

Do a search on Google using terms like "doberman pinscher" and "liver disease" and you will find lots of references. Here is one site with a good overview of liver diseases: http://www.lbah.com/liver.htm