Runners Knee...?

Lately for the past five weeks I have had a stiff knee in the morning. I thought nothing of it till two weeks ago; the pain was lasting longer through the day. Nothing to bad. I did a little research and I beleive I have runners knee. Couple questions though. If you have been affected by runners knee; how long did it last? What are some ways to treat it? I have used ice, and the icy hot gels. Also what are ways to strengthen, to prevent this again? Will this keep reappearing when I run? There is a 1/2 marathon coming up in fifteen weeks. Will I have enough time to get ready for it, or should waiting be the best? Also I don't if your like this. I think I am on running withdrawl. Ha. I feel really anxious. Is there any type of cardio activity that would be best, and wouldn't make this worse? Thanks for any tips. Have a great one.