There is a possibility of sprain in ligaments of knee joint which might be causing the pain.. may be in meniscus..
Next Steps
I will suggest you to avoid keeping knee in flexed position, avoid sitting down, avoid Indian toilet, avoid heavy work, use knee support, start hot fomentation, take analgesic like paracetamol for pain.
Health Tips
If pain not relieved, you may require some investigations like X ray or MRI of knee joint..