I'm right there with you. I've had thick slimy mucousy saliva since Covid last year. I was diagnosed with long Covid and went to the clinic last week. She explained that Covid can effect acid reflux and our gut and you can produce more mucous. I get choked on this stuff at night. I have tried everything. She suggested to elimnate all citrus fruits as that makes the mucous worse and eat as clean as possible. I do find eating salty foods makes mine worse for some reason. I went to 5 doctors, had my throat cultured and they could find nothing. I constantly clear my throat because there is mucous almost always in the back of my throat. I scrape my tongue every day to get the stuff off in the morning and use Peroxdyl by Colgate rinse. I too use Guafenesin daily and Astelin Nasal Antihistamine Spray (Prescription). The problem with an antihistamine for me is they are too drying for my eyes. I am so sorry you are going through this. Praying for you to get better right now.