I get cracking sound in knee when I climb stairs. Please help.

Hello doctor,

I am a 60-year-old, my height is 5 finch and 3 feet, and my weight is 145 pounds. I slipped three weeks ago stretching my left leg. There was pain on the left side of my left knee joint and below. I was able to walk but whenever I bend my left leg a crack or pop sound comes from the left side of the knee joint followed by pain around that region and below and difficulty in walking. I got hospitalized in the nearest hospital where I was given a few rounds of physiotherapy but after feeling a little better crack or pop sound kept on originating when I was getting out of the car, and climbing stairs (when my leg bends). Then on the suggestion of the doctor, I was given Synvisc one injection in the left knee joint one week ago. The crack/pop sound still sometimes comes with little pain around the left knee. I was looking for another opinion.