I was about to start the same thread today, but did a search first to make sure I did not get "Prerubed".
I hurt my knee this past winter snowboarding. It did not bother me until I started playing more disc golf as the weather warmed.
Went to doctors and I have a small tear in the cartilage in my knee. I was told to take it easy for a month or so and it could repair itself. That was working until I had to help my parents move. Twisted knee again and is very swollen. I may go and get it checked by a knee specialist.
Long story short - Get a brace, take it easy and if it does not start to feel better in a month, see a doctor.