How do I know if it is a strep, tonsillitis, or thrush?

Oral exam is needed. Tonsillitis is an infection involving the tonsils. Viruses are the most common cause of tonsillits, but several bacteria can cause tonsillitis. Strep is one of the more common bacteria that can cause tonsillitis. Thrush may be painful and most commonly looks like small white plaques in the mouth that cannot be wiped off easily.