Had surgery 5 yrs ago,but pain is back and getting worse whats wrong?

Im 22 yrs and having severe pain in my keen.5 yrs ago i had have ACL recons. and my meniscus repaired. When they repaired my meniscus they said it was very big tear only repaired cause of my age.For about the last 2 yrs its been hurting alot, when i bend of fully extend it, it pops and is very painful. Sometimes feels like its unstable and going to gie out. Im in the process of getting an MRI. What could this be? So far the only thing they have said it could be was another tear. Can a re-injury to my meniscus casue so much pain?