I have been on Lamictal for about 3 yrs. was up to 300mgs and now have been weaned down to 150mg. I've been fortunate, no major side effects, pdoc titrated carefully to my former full dose.
As far as seeing any "mental" change, it takes about a month, so do not despair.
Have you asked your doc about this? Maybe your other meds are re-acting with this?
Out of the various meds I have been tried on, Lamictal has been the best for me, but I know everyone is different.
Practically every med can have some side effects, many are only temporary, and some very mild.
The best response I can offer is that you contact the prescribing doc and talk to him or her.
Hope all goes well for you.

DE