History Of MCL Sprain In Knee. Swelling In Knee After Using Stairs. Help

Hello, I am a 19 year old female. Two years ago, I injured my knee playing basketball. I was diagnosed with a grade III mcl sprain on my left knee. I was diagnosed, however, without an MRI. I was in an immobilizer for six weeks, and on crutches, I was prescribed an external antinflammatory. Now, when I run, walk, or walk up stairs, my knee is fine. However, when I jog up a flight of stairs and sit down and relax for several minutes, when I get up my knee feels tight. It also gets swollen and feels like there in fluid in my knee. A noticable bump appears under my patella toward the inside of my knee. (After I was taken off my crutches, I was to do PT. I opted to do it on my own and never really followed through). HELP