Knee pain is a common complaint, especially as we age. According to the US Institutes of Health, "Knee pain usually results from overuse, poor form during physical activity, not warming up or cooling down, or inadequate stretching." Knee pain with calf swelling is a bad combination.
You may get knee pain for a variety of reasons. The most common include osteo and rheumatoid arthritis, sprains and strains from unnatural twisting and falls, bursitis and tendonitis, ilio-tibial syndrome, Baker's cyst, lupus, torn ligaments or cartlage, knee injuries or infections and knee cap dislocation.
Treat your knee pain at home. Elevate your leg whenever you sit or lie down, ice it, bandage it to reduce swelling and, above all, stay of that leg as much as possible. Take pain medication and anti-inflammatory medication if necessary.
Stay active and stay thin. Stretch your leg muscles and keep them strong. Use good shoes at all times.
See a doctor if you have pain during or after walking, both your legs are swollen, your symptoms do not improve after a week of self treatment or you have varicose veins. (reference 3)
Go to the emergency room if your calf is swollen and red and you have knee pain and fever. You may have thrombosis--blood clots in your veins--which can be deadly.