Excessive mucus in throat nose, continuing well after cold

Patient: Hello! About a month back I caught a cold, went through the usual and got better within the week or so. However, despite being better in every other area (coughing, sneezing, etc. are long gone), my throat continues to fill with thick phlegm that I can feel pool back up within a minute or less of clearing my throat that’s driving me crazy. On top of this, my left nostril — but only my left –is constantly full of thick snot. Much like my throat, the snot fills back up very shortly after blowing my nose and clearing it offers very little relief. So far I have taken a saline nasal spray frequently, which seems to thin the snot for an hour or two, but does nothing for the phlegm. I would try a more medicated nasal spray, but I feel it would only somewhat alleviate the mucus rather than get rid of the problem, and could lead to rebound problems if I rely on it too heavily. On the advice of someone who experienced something similar I’ve tried taking over-the-counter Fexofenadine tablets, and it has alleviated both the snot and phlegm a little, but not by much. I chose Fexofenadine over other similar products because I am currently taking Sertraline daily, and many kinds of decongestants and cold-relief based medicine can have serious interactions with it— Fexofenadine was one of the only ones I could find with no known interactions.I am not sure what is causing all this constant excessive mucus build-up, and would like to find a solution that stops it, rather than simply alleviate it a little, as it has helped very little.Thank you very much!Jess

Symptoms: Excessive mucus, constant phlegm and snot that will not clear in throat and left nostril, (post-cold) saline spray and fexofenadine have not helped