Hello dear...as you say same of your examination results normal..first you check your muscles strengthen is good or not for that once you visit physiotherapists...For detail examination...

Hii..considering your age. The possibility of weak muscles or bony changes would be negligible. If you are, or were a sport person, may be u have succumbed to certain injury which was unnoticed. I would recommend you to visit a physiotherapist for detailed examination or go for an mri. Hoping your knee will get back to normal very soon.

Knee pain at your age can be due to multiple factors. Your investigations and medications you are receiving are for Ankylosing Spondylitis. Ankylosing Spondylitis affecting knee alone is rarest as its affects sacroiliac joint and Lumbar spine more commonly. Well, you need a good clinical examination by a knee specialist. You may require MRI and some blood investigations. I hope that is bit helpful. Queries are invited. Regards