At 11 weeks old, I woke up to a very sick puppy, vomit, diarrhea, foaming at the mouth, trembling and seizures. The vet thought Stella had ingested something as curious puppies do, so they scoped her. Found 6-8 tiny pieces of black plastic/rubber substances in her stomach, but couldn't get them out, she was so small, only 4.5 lbs. at the time. Still to this day I don't know where that came from. So he did a gastrostomy to remove the particles. Ouch! The next day at the vet's office she had another seizure. They put her on phenobarbital. We went to visit her and I honestly thought about returning her to the breeder and getting another puppy, but my daughter started crying and tore at my heartstrings right in the vet's office. It was recommended that we take her to a neurologist because my vet suspected she had hydrocephalus (water on the brain). So two weeks later we did the MRI and she was diagnosed with mild to moderate hydrocephalus. I debated with many vets about the seizures being caused by what she ingested and they all said that was not likely and that it was due to the hydrocephalus. My breeder agreed to give us another puppy, through her tears and apologies, but I suspected she would have put Stella down as she would not be able to breed her. So we decided to keep her and do the best we could for her. I went with my gut and weaned her off of the phenobarbital a couple of months later because I always believed it was what she ingested. So far so good, she has been seizure free for about a year now.
I hope you are able to determine the cause of the seizures. As a side note, my mom had a dachsund that would have seizures about once per month. The cause was never determined and she recently just passed away at age 14! Good luck and please keep us posted on her progress.