I am sorry you are going through this. Adjusting is hard and will take time. Exposures can be precursor to what you are experiencing now. Have you seen allergy md or ent ? Sorry, i didnt read all the postings. I saw few people mentioned netty pot. I use it when i need to control phlegm. My doctor also rx- ed budesonide, i add to the rinse. I am attaching .pdf from Stanford ent as an example.
Did your allergy md do allergy skin tests to id if there are any specific offending agents in the environment?
There are multiple meds other than mucinex. Sudafed, flonase, azelastine, singulair, allergy shots :). Sorry its not easy and can be frustrating. Its hard to accept, but managing symptoms is what can help to improve quality of life.