Pit Bull is sick. Help Please?

I have a female pit bull up to date on shots. She has had a upset stomach with slight trace of blood in it and throwing up. 3 of my neighbors dogs have died the past week with the same symptoms. One of them took their dog to the vet and tested negative for parvo. So I am ruling that out due to she has been vaccinated and the other dog tested negative. I'm beginning to think someone has poisoned them. She is doing better than the other dogs. She walks around and wags her tail but shes NOT the same dog as usual. She is a little sluggish and won't eat drink or play. Is there anything to do for poisoning? The vets are now closed until Tuesday...