Sinus infection or something else?

For a little over a week now I've been so stuffed up! The thing is, it gets really bad at night and in the morning, but throughout the day not quite as bad, if at all. For awhile I thought it was allergies but the weather has turned cold, I can't imagine there is much in bloom now. Is this a sinus infection? I feel fine otherwise, occasionally have a slight sinus headache when I get congested but thats it. No sore throat, no fever, nothing. Whats wrong with me? Am I sick or just having an allergic reaction to something? I'm so tired of being so congested!!! Thank you!!