I'm 19, terrible knee pain, walking worsens the pain and causes locking and popping noise. xray normal mri normal. ?

Normal is good: So far, you have not done sufficient damage to show on imaging. That's good - but you are having warnings. Are you overweight? Is your footwear and/or gait correct? Can you try an elastic knee stabilizer and feel relief? Have you seen a chiropractor? Take care of these steps - if it's better - you'll avoid a bad x-ray down the road. Knees are delicate - you are right to take care of them.

Knee Pain: A locking of the knee would suggest a mechanical problem. Even though MRI testing is sensitive for evaluating the soft tissue of the knee, it can have false negatvie findings (miss pathology) and a normal MRI dose not definitvly exclude pathology. The persistance of this degree of pain despite conservative treatment and neg imaging would warrant a formal orthopedics evalaution.