I am sure you paid quite a bit for this dog.
If you do get rid of him and if you plan to get another dog. May I suggest you look into getting a Belgian Tervuren? - If you like Sheppard's you will adore a Belgian. Just make sure you get one from a very good breeder. Even a pet quality Belgian (with a neuter contract) will suit you fine and they love kids.
If you have never been around a Belgian Tervuren, then I suggest you visit a breeder some where in your area just to see what a great breed of dog they are.
http://www.abtc.org/ American Belgian Tervuren Club
My husband and I lost our Belgian about 2 years ago from old age. He was the most loving dog but was very protective of our property. He was trained to stay on our unfenced 5 acres of land and that was he did. Everyone that came in contact with him was impressed with him. They are extremely intelligent.
At some point in the future we plan to get another one.
I am sorry about your dog, but chances are more likely that he has some hidden illness that you are not aware of.
I am familiar with Belgian Tervurens. I admire their beauty but don't know much about their personality. But, just as with our experience with shepherds one never knows (probably about any breed). I know my aunt had several little dogs and they were aggressive and bit. We always had to be on the alert.