Waking up in the morning with mucus is a common complaint. There are a few causes of this, some of which are serious and require medical attention. I would recommend seeing your primary care doctor
who could further evaluate your symptoms and rule out serious disease processes.
Mucus is often produced because of inflammation in the sinuses, nose or airways. The most common cause of this every morning is because of an allergic reaction. Many people, even those without classic allergies, can have allergic symptoms. Common allergens include dust mites, pollen and dust. These are very common in bedding and pillows. Therefore a common story is that as you lay down to sleep, the allergens cause inflammation and therefore mucus when you wake up. This then resolves during the day as you are away from the pillow/bedding.
There are other causes of inflammation that you may just notice more in the morning. Most common is smoke. Smokers often have excess mucus production. Also polluted air can do this. Infections can cause these symptoms, but it is quite unlikely to have an infection for such a long time. Finally some lung diseases like chronic bronchitis
can cause this.
It might be worthwhile changing your pillow and airfilter. Regardless, I would recommend seeing your primary doctor to ensure there is no serious cause of your symptoms. Good luck.