You should get procyclidine for restless legs. I think lots of medication cause dry mouth. lithium is notorious. My quetiapine means I drink buckets too. But benefits outweigh the side effects which aren't that severe. Yesterday I had a tin of coke then a cup of tea and orange juice in a café and walking home I was still thirsty. But I do have a cold mind you. Sounds like you have quite a debilitating case of dry mouth though, ask psyche or doctor for sure