Vaccinating for parvo many times doesn't work and they get it anyway so since it's too late anyway don't go that route. Some feel the vaccination causes parvo and there is some evidence of that.
I can't believe you actually waited two days before doing anything, like consulting an expert. Oh, and vets are usually *not* experts.
There is something called Parvaid that works well on parvo, much better than anything a vet might give but you need to get it immediately to have any hope and you need to make sure the dog is hydrated. Easiest way to hydrate an animal that can't keep anything down is by giving shots of saline under the skin. This is not something an amateur should undertake by any means.
Why in the world would you wait all this time fora dog this sick?