My brother is a Respiratory Therapist and he explained it to me like this:
Smoking dries out your lungs. The body is alway producing mucous to keep things moving freely. Since all the years of smoking, your body has to "over-produce" the mucuous just to keep it at a normal amount.
Now that you've quit smoking, your body is STILL over-producing the mucous. That's what it is used to doing for years and years. And since you are no longer smoking, your lungs aren't being dried out. This causes quite a bit of congestion. ALOT of congestion, even to the point where your chest might feel heavy.
It does go away. But your body now has to get used to you not smoking. Probably will take at LEAST a month.
So.......hopefully you can hang in there and the congestion will eventually go away.
Good luck with the no cigs! Keep up the good work!