There are many sinus in our heads and some are toward the back. Something dripping down from the back sinuses will drain down the back of the throat. (Post nasal drip). This can be very irritating because it results in the tickle in the back of your throat that makes you cough. When this happen try lying face down, sitting back on your knees(in yoga this is called child’s pose) You may find it is difficult to breath through your nose at first in this position because all the congestion from the back sinuses drain froward from gravity. All this mucus plugs the small opening to the sinus and does not allow air to pass in and out. Unless you can get those sinus passages to drain properly, the mucus will fester and become infected.
Slowly take small sips of air into the sinuses by breathing in and out through one nostril at a time. You may need to take several deep breaths in and out through the mouth first to keep the oxygen flowing.
This may take as much as ten to fifteen minutes to completely clear all the sinuses.

Once you can get air in and out of each individual nostril, you may need to gently tug on different parts of the face to encourage the multiple cavities of the sinus drain. You may hear a whistling sound as the cavities open up. In order to get the last sinuses to open and drain you may need to gently “sip” when you inhale. This prevents the small openings to the individual sinuses from closing down from the pressure of too much air. You can breathe out more forcefully. This helps force the mucus out of the sinus.

Also I wear a nasal strip to bed at night to keep the nostrils open.
Of course the teas are necessary and using postural drainage in conjunction with tea to steam open the sinuses is extra effective.

I had frequent sinus infections for years. Now that I use this technique, they are rare. I will still occasionally resort to medication as needed, but I need them much less often.