Brigitte, I am going to refer you to a supplement that has helped me and many others. I am not sure it will help your dog, but try it. I have seen people's health turn around with this supplement.
The reason I suggest it for your dog is because my 8 year old Misty was acting a bit lethargic and not eating much of anything. I started giving her one pill a day and in less than a month she is eating well and is acting like a puppy. Again, this is just a thought, but try it. You should see some sort of a difference within a month.