Lithium only causes weight gain if it's affecting your thyroid - have your tsh levels checked. (mine shut down) but it also can affect the sodium in your blood, make sure you are drinking water- then you get water weight

I gained 30 on seroquel in two months. i went off seroquel and haven't lost much.
gained about 10 after starting risperdal in two months - went off that too
15 when i quit smoking...
lost a few pounds here and there. i go to the gym 4 times a week - eat fairly healthy

didn't gain on lamictal,
not sure about the trileptal...

i feel like once i gained the weight it just won't come off!! the seroquel was 2 and 1/2 years ago!