Hello, Knee pain is the result of an injury of knee or injury suddenly. It is vulnerable to damage because it takes the body weight and also the extra force when you run and also to overweight as well. It may be a simple strain because of stretching. If this is not relieved by rest and pain killers, the next alternative would be injury to meniseus damage as a result of sudden twisting or it could be Osteoarthritis where there is damage to the articular cartilage or might have developed from a popliteal cyst or baker's cyst or it may be due to torn ligament of tendon of anterior leviate ligament because of sudden change in dissection or twisting movement or if it is hot or red. With the above causes in mind, you better see your GP who can examine you physically in detail and also order for blood tests, X-rays and MRI Scan and advise the treatment accordingly including painkillers. Physiotherapy and sometimes-even artheroscopy can be useful. Hope this helps. Thank you.