Occasional left knee pain over the past six months is often due to minor strain or early joint wear like Osteoarthritis. Manage with rest during pain episodes, avoid excessive strain, maintain a healthy weight, and do strengthening exercises for the knee. You can use warm compresses and a mild pain reliever like Paracetamol if needed. If pain becomes frequent, severe, or associated with swelling or instability, consult a doctor for proper evaluation.