The pus pocket that is located near your tonsils (area between your tonsil and the back wall of your throat) is known as peritonsilar (near, around tonsil) abscess.
This, usually, follows tonsillitis (swollen tonsils) from an infection (in most cases Streptococcus bacteria) of your tonsils that has spread to the tissues around it.
Did you have red and swollen tonsil recently?
Have you lost your appetite or noticed that you don't want to eat or drink?
Are you experiencing trouble or pain with moving the neck?