Re: Why does my left knee keep doing this?
Okay, it sounds like your knee is unstable. It could be you need surgery, or it could be that correct rehab and exercises will make it stable again.
Don't waste any more time with drop in medical centers or emergency facilities. Go to a real orthopedic surgeon, preferably one who works with knees a lot. He'll do a physical exam and possibly an MRI to figure out exactly what's wrong and what the best treatment might be.