Hydration is crucial; especially if you live in the south. Make sure you're not mixing your sport drink too strongly. If so, you'll actually dehydrate by drinking it. The key to hydration is to drink BEFORE you're thirsty. It's a lot easier to maintain fluid levels than to replenish them. The latter has you playing catch-up for the whole ride... and the hours afterwards.

To attack the problem from a different angle; you did mention not being able to breathe through your nose.  If you want help in that area, try a breathe right strip.  They open up the nasal passages, especially helpful if that area is already constricted.  Common if you've ever had your nose broken.

So, did you open your nose and drink more water?  Are you still dry? 

EJ