Mucus is produced by many different tissues in the body, including the epithelial lining of the nose. A small amount of mucus is completely normal and helps with lubrication and protection of body surfaces. Nasal congestion such as you describe can occur when mucous production increases or also with vascular congestion because of inflammation in the soft tissue. This is most typical in the setting of an infection (bacterial or viral) or an allergic reaction. I understand that you don't have a cold or allergies, but sometimes the first presentation of a new allergy or a developing viral infection is nasal congestion.
There are several over-the-counter cold medications that you can try taking to help relieve the congestion. In addition, allergy medications (claritin or allegra) are also available over-the-counter. These medications may help your symptoms. However, since this is a new symptom and something you have not experienced before, the best thing to do is make an appointment with your primary care physician
so that he or she can take a more thorough history and examine you. There are several additional medications (including prescription steroid nasal spray) that can help with chronic congestion, so hopefully you will be feeling better before long. And, your physician can help you determine if this is a simple cold or if you need further evaluation. Please see your doctor