Pop in knee

Patient: Out of no where my knee started having an insanly painful knee pop whenever I would pull it up to fast. Then to get my knee back out I would have to force it through the pop again. Sometimes when I stand it feels like it is out of place so I have to get it to pop again and it feels okay.The only way to let it bend or to get it out after bending is to relax my leg and pick it up and move it with my hands. Why is this happening?