He has no fever and does not seem be sick by his behavior and she said that it might be worms.
You can't rule out worms with a single negative fecal sample. Intestinal parasites shed eggs intermittently. One negative fecal sample is good, but does not necessarily mean that the dog doesn't have worms. It could just mean that the worms were not laying any eggs at the time the stool was deposited. I work for a vet and we see dogs at least once every other month (often more frequently than that) that have a negative fecal sample the first time around but then on the second or third fecal sample we find parasites.
Have you taken a sample of the vomit in to your vet for them to do a gram stain to check for abnormal bacteria? Campylobacter is an abnormal bacteria that usually causes diarrhea and vomiting. But I have seen campy. in vomit samples from dogs with completely normal stools. Campylobacter is also a big deal because in addition to making dogs sick it is contagious to humans.
Likewise, your vet should also be running a giardia test on the stool sample you bring in. Again, giardia usually causes diarrhea but I have often seen positive giardia tests on dogs with perfectly normal looking stools. And, like campylobacter, giardia is contagious to humans.
The vet wants to do a blood work up, X rays, and maybe barium. I really was not prepared for this much cost this soon after adopting Oliver. I have until the 19th to return him to the shelter. If we return a sick dog I get my money back but it is his death warrant as the shelter is a kill shelter and they put sick dogs down right away.
We love this dog I got him for my 6 year old as a Christmas present but the whole family has bonded with the dog. He barks very little, is a little protective but not too much. He tolerates the cat and my 1 year old. We would like to do all we can before returning him but that does not include spending a couple thousand dollars before it is discovered he has a chronic condition.
I understand that money is always an issue when it comes to vet care. I also understand that when you bring a new pet home you don't expect to spend a lot in vet bills within the first week. However, and I am sorry to sound so judgmental, if you are not willing to spend the time and money necessary to diagnose and treat a chronic condition then perhaps a dog is not the right pet for your family. I understand that you expected to get a healthy pet from the shelter and that it puts you in a difficult position to make these kinds of financial decisions when you were totally unprepared for them, but really what's the difference between spending a thousand dollars diagnosing and treating a condition after you've had a pet for years vs right after you bring a pet home? You are either willing to spend the money to make this dog healthy or you are not. And if you are not, then you really have no place to put down the shelter for also not wanting to spend the money (of which they have little to care for a lot of animals) to make a dog healthy when they could use those resources for an already healthy animal.