What Causes Grinding Noise And Pain In The Knee?

Hello Doc I been having some really painful knee problems. About close to a year i had surgery on my Left knee i had an ACL Repair an a torn miniscus ...but before that i keep using my goopd knee (right knee) to support my self .So my problem now ,,My right knee hurts really bad i have some grinding noise when i bend it when am about to get up from a chair or couch it hurts so bad same thing when i want to sit i have to hold on to something near by to get up ..when i bend it hurts an sounds horrible an even feels vey horrible. When i go up stairs or come down stairs it hurts really i feel a grinding sound an i feel like something moves out of place..thank you so much for your time