I had the same problem. Lamictal stopped working, and I've been on Lithium for about a year and a half. Lithium, for the first two weeks was hell. I was so sick.
The nausea is gone (mostly), but the thirst never ends. My tongue is always so dry it feels sore.
I have thyroid issues, and my meds are constantly adjusted because of the Lithium.

I don't like Lithium, but it works for me