Have you talked to anyone about diabetes insipidus? It's not diabetes like the insulin kind, it is a problem where lithium messes with your kidneys so they don't hold onto electrolytes which is supposed to happen to keep a balance between what you are drinking and peeing. With DI you pee all the time and pee the electrolytes right out.

When I was diagnosed with it I was peeing every 45 minutes. I really had no idea of this. I went in to the doctor with UTI symptoms or something that made him want to urine sample and that showed the specific gravity of my urine was almost too low to measure. They did a few other tests and I took a med called amelioride that kept my electrolytes where they belong and I stayed on that until I came off lithium.

DI isn't super common but it's not uncommon with lithium either. I think about 10% of people on long-term lithium eventually get it. It goes away when/if you stop the lithium.