You could be allergic to dust mites.Dust your bedroom and wash the sheets, comforter, and curtains.Avoid using air freshner, strong perfumes. Remove wall/floor carpets. Try to replace all your pillows to hypo-allergenic pillows.My doctor explains, When you're asleep your body is reclining, so all the fluids from nasal passages drain to your sinus cavity, and when you sit up in the morning, your body has to clean it out..But still, the sure way to find out is go to an allergologist and also for proper medications.. I have allergy too, chronic one. I am currently getting 3 shots a month for pollen, dust and mold
I hope you feel better soon