Hello, I Have Pain In Both Knees, Especially The Left.

Hello, I have pain in both knees, especially the left. And swelling on the lateral aspect of it. It hurts to bend and I can hardly squat. The area that is swollen sticks out and feels squishy .
It happened one time prior- about a year ago. I had been very sedentary due to chemotherapy. When I became more active and returned to work both knees had extreme discomfort and swelling. I am wondering what this might be. I am 48 years old and female and have been healthy until breast cancer/chemo/radiation. Thanks!