I've been on Lithium about 3 years, and the dry mouth has not ceased. For me it's a side effect I can happily live with. I believe part of what causes it is that Lithium is literally a kind of mineral/salt, so it actually zaps the water from one's body. I certainly started to retain some water initially, but as BlueInanna said a lot of this subsides.

I pee a lot too, cause I drink a lot; I get all my levels checked yearly, and my sugar's always good.

If you can, try not to worry about that stuff for now....there are much worse side effects to deal with. And in my opinion there's a reason this med has been around soooo long.