Are you breathing through your mouth?Is a very dry mouth a symptom suffered by anyone else? In the summer heat, I could understand needing more water and a dry mouth but it's ongoing, especially at night. I drink approximately 6-8 large hi ball style glasses of water a day, around 2 1/2ltrs so, I'm sure I'm not dehydrated.
You could try Biotene mouthwash, it’s a saliva replacement and helps overnight, to see if it relieves things.