Peritonsillar abscess, also called PTA or Quinsy, is a recognised complication of tonsillitis and consists of a collection of pus beside the tonsil (peritonsillar space). Basically an absess. It causes great pain, fever, malaise and is associated with tender, swollen lymph nodes.
Sore throat is a common complaint. It is most usually caused by a viral infection, but occasionally by a bacteria called streptococcus, so called 'strep throat'. Strep throat (or "Streptococcal pharyngitis", or "Streptococcal sore throat") is a form of Group A streptococcal infection that affects the pharynx. The signs and symptoms of strep throat are red, sore throat with white patches on tonsils, swollen lymph nodes in neck, fever, and headache. Nausea, vomiting, and abdominal pain are more common in children. The patient will usually not have a cough, unlike in a viral infection or coldlike symptoms including stuffy noses and sneezing.
I believe Quinsy is the more serious of the two and may need antibiotic treatment.