Could be various things:
2) Allergic reaction to dust mites: Some people still have reactions to dust mites even though an allergy skin test shows a negative response. If you haven't already, purchase a mattress protector which completely seals the mattress along w/pillow protectors which are zipped and exposes no pillow (including the one your spouse sleeps on).
3) Sinus drainage: Zyrtec works great on my sinuses.
4) Night cream: Do you use a moisturizer at night that you don't use during the day?
Hope this helps & you feel better soon.