BAD TASTE IN MOUTH AND MUCUS IN THROAT

My adult son is very concerned about the following symtoms (symptoms):  Mucus in back of throat, but no sore throat.  Has bad taste, like something relieved itself on back of tongue.  Feels like he has bad breath, but he does not.  He took a cotten swab to the back of throat and removed a patch of mucus.  Later took a drink of cold beverage.  Liquid fealt colder in the place he swabed.  On the very back of tongue, he has flat clear blisters.  He has had them for a long time, he says he can't remember when he didn't have them.  Tonsils removed when he was 2.