I have clear sticky saliva that gets stuck in the back of my throat since Covid last year. Its worse first thing in the morning. It wakes me up at night. This is NOT sinus drainage. I've been to 5 doctors and had my mouth cultured. All came back normal. B12 was low. I rinse my mouth a lot, scrape my tongue to get this stuff off several times a day and drink a lot of water. I was told to use Listerine to keep bacteria done. I have been on so many things and nothing has really helped. Personally, I think this is due to long Covid. I have been battling this since Oct. 11th of last year. Praying for you and I am so sorry you are battling this.