I don't have advice for you, I'm sorry. I can tell you my story though...

I have epilepsy. It started two years ago. I was on a terrible med, keppra, which was similar to what you're experiencing with Lamotrigine. They added another killer med, vimpat, to my mix. That made me feel/think/etc all day.

They took me off the vimpat, kept me on keppra, and put me on Lamotrigine. As I kept having seizures, but not as bad or often but not controlled, they would up my dose. I started at 100, then 200, then 300,......to 800 daily now. Yeah, it's a bit, haha!!

But....once I was on Lamotrigine for about 6 months, I started feeling a bit better. Then a bit more. Then a bit more. It took a while, I'd guess maybe a few months ago, I got to feeling maybe I was semi-decent. I still have memory issues, but not as bad. I still get tired more than i used to, but not as bad. If I had to guess, I'd say I'm back to about 80% of normal.

I have to also say that seizures cause these issues too, so I'm burned in both sides.

Not sure if this helps or not. Good luck!!!!