What Causes Pain And Tightness In Left Knee?

Several years ago I slipped and fell and twisted my left knee badly. It took about half a year to recover. Few months ago, during the cold spring weather I would frequently sit cross-legged for long periods when using the computer everyday. I sat like that until my knees began to hurt. But I ignored the discomfort and continued sitting cross-legged for long periods. Then I moved some furniture. After that, my left knee began to feel more and more uncomfortable. One day, I wanted to squat down and there was intense pain in my left knee when I tried to do that. Before it could heal I strained it again recently. I do not know which part of the left knee is giving problems. It feels tighter. I may need to kick it a little several times a day when it gets uncomfortable. When I kick it there is usually a sound. Age: 51+ Height: 5 feet 7 inches tall. Weight: around 120 pounds