Some good ideas here.
What you need to do is to see a freekin' doctor already...
This could be a symptom of a medical problem. I just did a search for "dry mouth" on webmd.com and came up with this:
http://my.webmd.com/content/article/...tselectedguid={5FE84E90-BC77-4056-A91C-9531713CA348}
If you drink enough water and breathe through your nose and STILL have a problem, then maybe it is a drug you are using - even overthecounter ones?
Don't go overboard on the water thing though. There is an incredible amount of mis-information - even in this thread already - about water intake. See here:
http://www.snopes.com/toxins/water.htm