Sinus problem since 3 months will definitely need more than nasal drops. If its only blocked nose then nasal drops for few days is fine. In your case you might suffering from other symptoms as well. Steam inhalation can be tried.
If its affecting your day to day working etc it will require examining by an ENT specialist and/or CT scan of nose and sinus.
Next Steps
Consult an ENT Surgeon online/ personally
Health Tips
1. Sinus infections left untreated tends become chronic.
2. Excessive use of nasal drop is not advisable, it can damage nasal lining.