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Well as you describe,post nasal drip(excessive mucus production in sinuses) can cause such phlegm at back of throat and it later results in such sensation.
You should do saline gargles and steam inhalation.
OTC Claritin can be tried.
Also avoid spicy,greasy,fried foods for a while.
Start a multivitamin containing B complex.
Vitamin C lozenges can be helpful.
Drink warm liquids,soup.
Elevate your head while sleeping.
Use a humidifier in your room.
Take OTC Prilosec.
If your symptoms'll persist then consult your doctor for further evaluation and management.
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