Your doc jumped right to full dosing, and didn't titrate in 25mg increments? Most pdoc's titrate to help reduce any side effects and to arrive at the lowest therapeutic dose, hope all goes well for you, it is really agreat med for Bipolar-II.
They have been using meds for epilepsy for migraines, and Bipolar, probably other disorders too, that I have yet to read about. I do not know the technical answer to "why?" they are using it for various things, but it is the way the med effects the brain's "electrical firing" I guess sort of like electrical current balancing, affecting neurotransmitters?
Perhaps one of our psychopharmacologists can provide you with the real technical/scientific explanation, I'd copy it here from my various sources to help, but I have to get on the road.
My brother says he's doing well with it as he's weaning off his long time succesful med.
I wish you luck with it.
Oh, and again my lack of libido issue has nothing to do with me being on Lamictal, it started way before any of the meds I take, plus for me, my sanity is more important.