Mucus production is one of the body's main defense mechanisms against infections, dust, and other things in the air. The mucus works by trapping any particles you inhale and keeping them from getting into your body.
Unfortunately, there are several situations in which mucus production may be in overdrive. The most common, in the absence of cold symptoms, would be nasal allergies or sinus congestion. Both of these cause the lining of the nasal passages to become inflamed and produce excessive mucus.
Based on your symptoms, I would recommend that you start by getting evaluated for this allergy problem. You could go see your primary care doctor
, who will be able to take a good look inside your nose and throat and help figure things out.
If you do turn out to have allergies, this is usually a problem that can be easily controlled with common medications, such as non sedating anti histamines (think of Claritin, Allegra, or Zyrtec), as well as nasal steroid sprays which are available by prescription.
Your doctor will be able to make some recommendations about how best to treat these symptoms. With adequate treatment, I expect that you will be improving before you know it!