Dog will not eat and is vomitting

Question
I have a 4 1/2 year old lab/terrier mix. He has not ate his food in 3 days. He is trying to drink water, but he throws it up very shortly after. It is obvious that he does not feel well. What could be causing this, and should I take him to the vet?

Answer
Does this dog eat bones or rawhides and stuff? He could very well have an obstruction in his bowels or his stomach. Any time a dog vomits for three days and especially water he needs to be seen by a vet. By now he is probably very dehydrated also, which will then make him worse.
Get him into a vet's tomorrow if you can.