I think he is poisoned, if you say that 3 days ago started feeling these simptomes then you should take him to the vet, maybe the doc will do some stomach washings, though I don't know if it will help now. Milk usually helps in these cases, but only in the first days...
I know that, because I had like two dogs which died because my neighbour poisoned them with rat posion and had the same symptomes. The deathly period was about at most 1 week. I wish well for your dog and maybe he will get better.
