I'm new here and I'm sorry I didn't get to read the whole thread. I just thought I'd tell you a little bit of what I learned from a dog with seizures and maybe some of it will apply to your situation or maybe not.
My boyfriend and I have a dog we got from a rescue group, he had been a stray, he was about a year old when we adopted him. We had him about a month before he had a seizure, we took him to the vet, they said watch him, he continued to have seizures, originally one a month and then more and more often. We put him on potassium bromide, seizures continued and the vet added phenol barbitol (I think you mentioned this last drug).
My dog probably has/had epilepsy but this is what I learned over the next few years (the dog is about 9 now) chemicals, preservatives and stress set off the seizures. I learned all of this the hard way, I inadvertently gave him seizures by giving him rawhide which had preservatives, using a different carpet cleaning solution, bits of food that I was eating, various things. I had to link all those things to his seizures. So we've learned to eat foods without preservatives (healthy for him and us too) use green cleaning products or things we naturally have like vinegar and baking soda (on surfaces the dogs walk or lay on), no pesticides are sprayed on our yard and we do have the exterior of our house sprayed to prevent ants but the dogs aren't permitted outside until 4 hours after the application.
The phenol barbitol can make them sleepy and kind of listless, we tried to keep it to the smallest dose without him having seizures. Just this past year with the vet's approval he was taken off all medication and so far it's been fine (it's been about 6 months). I just wonder if we could have taken him off it a few years ago. I used to feed him prescription food for a sensitive stomach but actually have had better results (less stomach upset) with premium foods. I currently feed the dogs Innova (dry) with various premium wet foods mixed in, sometimes a little organic cottage cheese or yogurt.
So I don't know if this is helpful or not but it took me a long time to connect the preservatives to the seizures in my dog. The carpet cleaner I discovered pretty fast, I had to clean all my carpets again just a day after doing it. This may have nothing to do with your situation but maybe something will be helpful to someone on this board. Best of luck to you and your puppy, Hope.
Just because there are no worms in the poop does not mean the dog does not have worms. Take it from somebody who has been there. 