Here your knee pain could be due to multiple resion like vitamine D and calcium deficiency , it can be osteo arthritis of knee, it can be only knee cap movement disorder, or it can be combination of all above. Now what ever is the cause of knee pain I suggest you should visit a ortho and physio for proper check up and examination. Do needed test like knee x-ray and MRI scanning if needed. Now plan your treatment as per the diagnosis. For minor to moderate problem doctor will suggest for physio and medication. This will help you to get pain relief. Also do regular knee strengthening exercises as per suggested by physio. For major damage in knee doctor will suggest for surgery only it can be corrective or replacement of knee joint. Again the physio has to be continued for further rehabilitation. Here I suggest one more thing avoid weight bearing exercises like walking, stair climbing and standing for long time. And focus more on exercises. You can also do cycling as a exercise to burn calories and improve cardiac endurance. Also use hot and cold pack frequently for some more pain relief. It will be helpful for you if you follow guideline step by step. Take care.