My toddler kid got that long lasting mucus crud. It was likely enterovirus, as several kids at daycare got that diagnosis around the same time. Took about 10 weeks to clear on its own.

I have it now (no other signs of illness). One of the best things you can do is keep your sinuses clear, since that drains into your chest. Cut off the source and your body can work to clear out the reserves. Take a decongestant daily and do a sinus wash with saline solution and a little iodine as often as you need. You might have to do it 4 or more times a day to start but once your sinuses are clear once a day should be fine. If you're really congested, double up the salt for a bit as that will encourage better drainage. Be careful about putting too much pressure up there. Enterovirus can also cause ear infections and inflammation in the ear canal.

Mucinex and bromelain can help with mucus. Quercetin works as an anti inflammatory and antihistamine if you need some pain relief or to cut down mucus production. Stack with Q with zinc if you think this is viral and you need some immune support. Vitamin D and C wouldn't be a bad idea, either.