Im 19, an athlete. im facing a tingling-like feeling o my right knee, it only happens when i hold my muscle and never when my muscles are relaxed. its just uncomfortable. it feels like the pain inside the knee, on the patella, no pain while i run?

If you don't have pain when you run, this is unlikely to be a significant structural problem. However, I would recommend that you keep a written log of when this is happening and then see your doctor to start (and maybe an orthopedist) to have a complete exam and possible MRI to diagnose the problem. The doctor may recommend some strengthening exercises and/or physical therapy.