At the time your symptoms began did you have a head injury… even just a little bump that you shrugged off??
Please know I have no medical training whatsoever. This is from my own experiences and my research.. which it has been a long time since I have I done research. Today my time is limited because of grandchildren. .. so some more research on your own needed.
If allergies or environmental irritation from what you breathe in then saline nasal rinses should help along with allergy medication. Instead of the nasal rinse or neti pot that you have to mix I have been using Arm & Hammer Simply Saline nasal mist. You can mist it in or use it like a nasal rinse. I used it this morning .. along with my nasal antihistamine spray. .. and the nasal drip stopped. I will do the same this evening. If I get drippy or stuffy between times I use the saline spray. It washes the irritants out and moistens the nasal passages. a lot of times our nasal passages are dry and the mucus … aka snot.. thickens and gets stringy. Sometimes only one side.. for some odd reason. Many sites will tell you how snot forms… just put in your web browsers search engine “ where does snot come from” .. you will even find videos.