Suggest Treatment For Phlegm Stuck In Throat

For over the past year I have had a problem with mucous stuck between my nose and throat at least 3-5 times per week. After excessive snorting sometime for more than a day, when it eventually comes out down my throat, it is a large clump of mucous and is usually green, brown or greyish looking and is about the size of kidney or great northern bean. At times, it chokes me enough to cough and gag it up. When this happens it usually has a hard part in the mucous that scrapes my throat. Why is this happening?