Severe pain from the knee to ankle that worsens on standing/walking and eases with rest may be due to nerve-related pain like Sciatica or a blood flow issue such as Peripheral artery disease. Avoid prolonged standing, take rest, use warm compresses, and you may take Paracetamol for temporary relief. Since it has lasted two months and is severe, consult a doctor for proper examination and tests to confirm the cause and start targeted treatment.