Sure sounds like you might be getting Keto flu. If you've been drinking that much water, you've definitely been flushing electrolytes out of your system. Drink some bone broth or consomme, or chicken or beef stock with a tsp of salt salt stirred in. You can also stir in some melted butter to make it taste even better and to provide more fat.

Have faith that the keto flu is only temporary! Within a day or two, as your body becomes accustomed to burning fat, you'll start feeling TERRIFIC!