OtoHNS_MD is right, salt water irrigations are very helpful. follow the instructions on the box. you'll rinse out all of the junk.
MrsKett is right, it's uncomfortable, but afterwards you feel so much better.
mucinex is long-acting guaifenisin, which is a cough treatment, which won't help the nasal drainage.
Good luck quitting smoking!
The salt water irrigation is an interesting experience - you will pour a bottle of saline solution through one nostril, and it will come out the other, and your mouth (while over a basin). It is uncomfortable at first, but it helps greatly with allergies and sinus congestion. Give it a shot. Also, grab some Mucinex. Good stuff, and it will help clear and move the congestion. Hope this helps.
Congratulations on your decision to quit smoking.
What do I do with the salt water irrigation?
Woke up today with green mucus congesting my throat and nose area.
You could try over the counter salt water irrigations (I like Sinus Rinse, but there are a lot available). If it persists, you should see an Otolaryngologist (ENT surgeon).