Prognosis for a Puppy with Parvo?

Our 12 week old toy Poodle was diagnosed with parvo 6 days ago. When we sent him to the vet, he was lethargic, had no appetite, and had watery poop, but with no blood. 2 days later, his poop had a few signs of blood and he is still vomiting. He was injected with the serum which kills parvo only once since he is still too weak to take the second shot. Forward to 6 days after (which is today), he is still very weak and has no appetite. Yesterday the vet said he vomited twice. But he no longer had blood on his poop though it is still watery.

Is this a regular cycle for the battle against parvo? Or is 6 days too long? I am sad for him since he is staying at the vet and we only visit him twice or thrice a day since we have work. What should we do next? I just want a big amount of hope that my puppy will survive and his stay at the vet will be worth it.

Thank you so much.