There are many possibilities that can cause your persistent knee pain
Any of them ranging from problems in the knee and around the knee to from the back or even a systemic issues. Unfortunately, the best way to help you with firming up a diagnosis is a proper history and physical exam. Proper testing is helpful, and sometimes proper testing means testing areas that don't immediately seems like the sources of pain. There are some non-interventional (proper medications, proper pt, etc) and interventional (injections under xray guidance) that might be helpful.
Hope that helps you have hope that someone near you can diagnose it more accurately.