I have pains in the sides of my knees?

Long list. Pain can also be referred from back or hip. Common inside knee pain could be due arthritis, medial meniscus tear, strain of the ligament (mcl), inflammation of hamstring tendons, bursitis, plica, or knee cap region wear/tendonitis. Pain outside may be due to arthritis, lateral meniscus tear, strain of ligament (lcl), itband syndrome, popliteus tendinitis, knee cap region wear or tendonitis.
Variety of causes. Knee pain can have many causes. Whether the onset is acute or gradual or related to injury or specific activities can help us narrow the possibilities. Age of the patient and prior knee problems also give us clues. If >50, then meniscal (cartilage) tears and osteoarthritis are the most likely causes. Patellar tendonitis, patellofemoral & it band syndrome are common in young & active patients.