Sinus infection causes postnasal drip that is an extremely common problem which happens because of excessive production of mucus from nasal mucosa. It is uncomfortable and irritating under any circumstance which can impact people of all age.
Mucus is produced from glands which are the lining at throat, nose as well as airways. It is the wet and thick substance which help cleans and moistens nasal membranes, captures and gets rid of inhaled external matter, combats infections as well as humidifies air within the airways.
The symptoms such as under normal situation, you will not pay attention the mucus in your nose because you often swallow unconsciously during the day. However, when it is produced excessively, mucus will drip at the back of your nose, trigger postnasal drip.
Some other symptoms of postnasal drip can be sore or irritated throat, hoarseness, coughing, trouble with swallowing, congestion as well as feeling of weakness.

I have some simple tips for you, hope it helps!
1. Gargle with warm salt water. This can thin out the mucus, thus easier to expel and be able to flush out other irritants from nasal passages.

2. Steam inhalation (Small children are not recommended for applying this tip): Take a bowl and fill with hot boiling water. You can add any essential oil if you like. Place a towel over head and put your face above the bowl. Breathe in deeply the steam for at least 10 minutes and then blow out the nose.

3. You can take few drops of peppermint oil into a piece of clean cloth (after soaked using warm water), place near the nostrils and breathe in its vapors. Apply this regularly.