Generics have to be on a 20% Range of the brand name. Meaning it can have either 80% or 120% of the active ingredient. Of course, they lean toward 80%.
I had the same situation. And the change was supposed to be for the better. (Teva)
I will omit the story but run, don't walk to get the same one you were on.
Many phyc meds are finnicky. Lamotrigine is one of the most.