Even though all the symptoms was spot on by Dr. Google, i'm still gonna consult my physician to be sure. If you are in a similar situation, i advice you to do the same. But still, the internet is a thing of wonder when it comes to finding great things (although you sometimes have to sort through a lot of garbage to find the nuggets of gold). Be thorough and critical though.
The pain (for me anyway) is not so much in (or behind) the kneecap it self, but the top outerside of the calf and towards the backcenter of the knee.
When i sit down on my knees and play with my little son, it hurts after a while, and when i sit in the same position on a chair i have to shift legposition after a while. But when i run og cycle it isn't that bad. I played basketball a little week ago with the kids at my work, and that was definitely a mistale (before i consulted Dr. Google!)
The remedy apparently is:
1. Rest
2. Ice
3. Stretching
4. Strengthening of muscles (Quadriceps and Gluteus Maximus)
5. NSAID or other anti-inflammatory medicine like ibuprofen or aspirin
If you want to do cardio, you can swim with a pullbuoy (that prevents your legs from bending and aggravating the pain and injury) When the pains subsides, you can start running for short distances on soft ground and be careful not to start with too long running sessions and too often.
But to be sure, i advice you to contact a physician to be sure if you think you have Runners Knee (or any other pain or injury!).
But as i said in the beginning there a many good sites, where you can get an description and advice regarding runners knee - One of these online-places are the "Sports Injury Clinic" where you can get a description (symptomes) and get advice (with film) for streching, massaging and strengthening exercises).
So - If you are in my kind of situation with a runners knee, be patient and grateful that it is something we can do something about, and hopefully before too long so my tri-training doesn't suffer too much! :-)