I have no clue as to what could be causing the fits, but unless your vet has done extensive testing and still can't find the cause, I would switch vets. Your dog is too young to just chalk it up to being nothing.
Are you describing a seizure? How often have these happened? I agree with lindapalm that this is something to be concerned about in such a young dog.
Has he always had these fits? When was the last time his veterinarian saw him and was any bloodwork performed?
Yorkies are an at risk breed for liver shunts that could cause these types of symptoms...how does he do otherwise? DId he gain weight normally as a pup?
Another thing to do is to post your concerns in the Expert Ask A Vet forum. There are several discussion threads already going about seizures in pets. Our veterinarians can help you by suggesting questions for you to ask your veterinarian and possibly even make a recommendation to another veterinarian if appropriate.
whatever you do or dont do, make sure he is eating!!!!!!!!! force feed him, syringe feed him, you need to get nutri-cal a vitamin supplement for pets who are not eating or who just need extra help and energy. i have a yorkie also and when i first got him he was hypoglycemic and i guess you could consider it a fit he would bob his head for a bit and then just basically pass out, i would pick him up and he would just fall back down. you should take him to a vet, but whatever you do make sure he eats and stays hydrated weather he does it on his own or you do it. yorkies are such little dogs and need all the nutrition they can get
Did you get papers with your dog? I know this is a bit of a controversial question, but about six years ago I got a beautiful collie/shepherd mix from a breeder out in the country. He didn't give us any papers and the dog was fine until he was just under a year old. He started out having few seizures and then they soon got closer and closer together.
We took him to the vet and got him medicine for epilepsy. This helped for a week or two maybe, but then the fits started back up.
Unfortunately we had to put the poor thing down, the vet said the medicine was the only option and if it wasn't working we shouldn't let him suffer. We now think he might have had a brain tumor and not epilepsy and that is why the medicine didn't help.
HOWEVER: he never went through stages of eating, but it's my understanding that dogs wont eat if they are too stressed, which may be caused by it being sick.
You might have a dog that just came from a bad breeder, or you may have a dog with epilepsy, which means it can have a fairly normal life if you give him his pills regularly from what I hear. Take him into the vet and try to calm him as much as possible.
Remember- it doesn't matter what he eats right now as long as he eats something in the beginning.
I hope this helped and/or you figure out what's wrong and he's ok soon!