That's so sad. It's really hard to watch them suffer. We once had a dog that was older than me. Before we put her down, she was deaf, blind, had a tumor, and the day before we put her down, she had a seizure that paralyzed her leg. She was 15 when we put her down.
We've also had a little puppy that was silky/yorkie mix. We unknowingly got him from a puppymill, and he was very young. He had cocciddia and Parvo. That's also very sad. 2 days after we got him, he started getting sick. My mom had to force feed him baby food and pedialyte all day and night. All he would do is throw up. Needless to say, we had to put him down. All and all, the vet bills came to $200 and even though the breeder gave us the puppy cost back, she wouldn't pay for the medical bills. We were so scared that there was parvo in our house that we bought all this stuff to kill it. Well, I guess it worked because we have a Yorkie pup and a maltese pup and both are healthy as horses.
I'm really sorry about your dog. Maybe it is his time to go. I always think that when one pet dies, or is dieing, God has another pet out there who needs you to take care of and love him. Thats the situation I had when my dear Oliver died. Little did I know, that around the day Oliver died, the shelter had just gotten in Misty. Misty is my biggest baby now, and I thank God not only for the time I had with Oliver, but for my new found love.