I have a large bump on the outside of my knee and sometimes get a random pain in the back of my knee. My knee is also very tight. I did not fall but I do play basketball for 2 hours every day. The "bump" has been there for around 2 weeks now and seems to be getting larger.

Is it soft and squishy or hard? You could be leaking fluid out of the knee, which like all major joints has a membrane filled with synovial fluid to lubricate it. If you near one, a sports medicine clinic would be best. Get it treated sooner rather than later if you want a knee that doesn't lose it's fluid altogether. The fluid does regenerate but there's a limit to the ability to repair the membrane.