Suggest Treatment For Loose Knee Caps With Pain

Hello, I am 29 years old, about 120 lbs, and 5'2. I have had "loose knee caps" all my life. I dislocated my left patella about 5 years ago, but did not need surgery as it went back into place. Recently I was walking and my left knee cap shifted out of place but went right back in. Now I cannot straigten my leg all the way. I am not in as much pain as when I dislocated my knee 5 years ago. But I cannot walk very well and have pain and tightness in the side and back of my knee. Any advice?