I have the same problem, especially in winter when I tend to easily become dehydrated. Trapper's salt water gargle will help remove the thick mucus. I wanted to suggest a mucus removal fast that really helps me when things get very bad. Its very simple to do, but you do need three days where you can be at home for the most comfortable results. Every morning drink two cups of prune juice. For the rest of the day alternate drinking pure water and apple juice. Do not eat any solid food at all. However, if you simply cannot fast, you can try eating a few raw apples chewed until they are liquid in your mouth. This fast helps push mucus out of the body. While you are doing this, it helps to keep a vaporizer going so the steam can help loosen mucus in the sinuses. This is a rigorous three days, but the results will last a long time. If you discover the foods that tend to produce the most mucus in your system, then you can either reduce or eliminate them altogether.
Remember that mucus is a natural and necessary part of our system, without it we would die. The thing is to produce only the mucus we need for proper digestion, breathing, lubrication, and elimination. The excess, caused from some factor that irritates the body and causes even more mucus to be produced, is what we must learn how to control.