It's common name is runner's knee. I have had it for two years now and its a tough one. Here is one of the best sites out there that covers all I have learned about the injury: http://www.drpribut.com/sports/spknees.html
Take care of it now or it will just get worse. I have the time to ride 4-5 days a week but this injury limits me to 2-3 usually.
In my case, tight hamstrings and flat feet (no arch) were the main causes. Solution was to stretch the hamstring and wear orthotics.
And studies have shown that cortisone shots reduce pain over a couple of days or weeks but increase cartalidge deterioration in the long run and from all I have learned are not recommended unless you are a pro and there's an event coming up like the Olympics (see Hannah Teter's experience last Olympics.)
As everyone always says, see a doctor. Most knee problems are lumped into runner's knee, but you may have another problem that only a doctor can diagnose in person. If you like to wakeboard, don't neglect this injury.