Send blood or throat swab
for culture and antibiotic sensitivity. Need
to do antiseptic mouth gargle
to take care of source of infection.
There are other causes needed to be ruled out are laryngo esophageal reflux, irritative pharyngitis (due to dryness of throat), certain chemical exposure, other source of infection etc... If chronic tonsillitis or hyperplastic tonsil then tonsillectomy will help. Acid reflux needs a treatment with antacids and proton pump inhibitors.