Thanks for posting your query.
Since you are only of 19 years old,throat infection
as well as tonsillitis
may be caused due to-Impacted wisdom tooth
which is inflammed.
I would advice you to get a thorough clinical evaluation done.
The impacted wisdom tooth has to be extracted or flap overlying tooth has to be removed.
Take complete course of antibiotics-analgesics.
Gargle frequently using warm saline and betadine rinse.
Maintain oral hygiene