Since you have had no relief after 7 days of taking montelukast, please consult a doctor immediately instead of self-medicating. A persistent sore throat may indicate a viral infection (which antibiotics cannot cure), a resistant bacterial strain, or another underlying issue. A physician needs to examine your throat physically and may recommend a throat swab. For temporary symptomatic relief, try warm salt-water gargles, stay well-hydrated, and take over-the-counter paracetamol for pain if needed. Do not start any new antibiotics without a proper medical evaluation and prescription.