I have an epileptic husky, Yukon. Similar to Jax's situation, Yukon was about 1 1/2 years old when one night he was sleeping and went into a seizure, that was in November 2013. He had 3 or 4 more before I took him to the vet. They also ran tests and could not find anything wrong and diagnosed him with epilepsy and put him on phenobarbital. He was seizure-free for about 7 months before he had another fit, and then a couple months after that when it became worse. The vet put him on Keppra as well, and eventually also put him on Zonisamide and Potassium Bromide. That seemed to help, but he would still have breakthrough seizures. It would vary, from one every week or so, but at one point he was having cluster seizures (3-5 grand mal) every couple of weeks.
In February this year I started him on CBD oil, and the vet also suggested Purina Neurocare. For the first few months I did not notice a difference. He would have 1 seizure per week. However, since about June he has only 1 seizure about once a month, which is a huge improvement. Now, I usually and skeptical of special foods and if they work, but I will say that I do think that this food does work. I thought it was the CBD oil, so I have been weaning him off the Neurocare (mainly because it is $50 per 11lb bag and Purina stopped offering discounts), but since I started doing that he had 2 seizures in a month. So, I am going back to putting him on the Neurocare and continue the CBD oil.
That food is prescription only so I would talk to your vet about that. I also have a couple places I get CBD from ( I use a combination of oil and CBD biscuits). I can give you my facebook profile or contact info if you need more advice. I have been dealing with this ugly disease for 5 years now so I can completely understand how you are feeling. There will be ups and downs, just when you think things are looking good you have some bad days. It's heartbreaking to watch and it doesn't get easier but you can manage it and he can have a happy, healthy life.
Good luck to you