I had increasing problems with my sinuses over several years. It got to the point where I hadn't been able to breath through my nose for months. My co-worker took to calling me "Darth Vadar" because of the awful sounds I made...
As everyone has said, there are various things to try:
1. Sudafed, or other over-the-counter sinus medications. Combining with Ibuprofin will help reduce swelling even more.
2. Antihistimines - will help only if your congestion/inflamation is allergy-related. I take Zyrtec daily, but different antihistimines work for different people. If I could handle the drowsiness, good ole Bendryl is amazing and one of the most effective on the market. I still resort to it when I have a bad allergy attack.
3. Neti Pot, or other sinus rinse systems - I tried this, but my sinuses were so inflamed I couldn't get the water to flow. But my doctor finally started to take my complaints seriously when I told her I had tried using a Neti Pot for weeks but just couldn't make it work. I think Doctors realize you are truly desperate and aren't just complaining about a minor problem when you voluntarily try a Neti Pot!

4. Nasal steroid prescription medications - Flonase is the most wonderful drug ever.

Within 4 days of starting it, I was breathing again. I use it once a day now, and haven't had a problem since. There are several other drugs in this same class (Nasonex, etc) each with their own pros/cons - you and your doctor may need to play around to see which one works best for you.
Also, it is possible (although not common) to have a sinus infection that doesn't cause a whole lot of other symptoms. In this case, antibiotics are needed. My doctor put me on a round to see if that was the cause of my problems, but they didn't do a thing, so we went onto the Flonase.
So try #1, 2 and 3. If the problem doesn't clear up with those, go see your doctor.