Thanks for your query,
since your child is having fever
for last 4 days and now he is having acute pharyngitis
as well,so i advise you to take him to pediatrician
as he may need a course of antibiotic .
In the meantime give him paracetamol
every 6 hourly till fever is below 100F,do tepid sponging.give hi plenty of fluids,warm water will be soothing for his throat pain.
also give him mixture of ginger,honey and lemon water,
Your son will be fine