I am a physiotherapist and of course it's hard to make a diagnose over a forum
I don't know in what kind of condition your body is.
How about your stance?
If your bindings are not well placed it can give tension to the upper leg. What is good? Natural stance! Do you have that on your board?
With holidays its always the same, sore body but its the recovery that shows how well trained you are.
Im in good shape, workout at least 4x a week...but this knee thing is constantly around.. I think my stance was too narrow, or the angle was not ok. I have a new board with bindings that are angle adjustable. Hope it will be different.
I have a appointment at the doc next week..i have to take care of this...hate being injured/unable to kite :S