Dear Juan,

I am not certain when you posted here or if you have found a reason for your knee pain. 

However I am the Mom of a 15 yo whom is also having knee pain.  I am not certain that this is a proper diagnosis for us (Oshgood-Schlatter Syndrome) but it may be a direction you can take for your own search. 

Whatever the cause, you may find some relief by stretching out your legs (look for knee stretching exercises) before activities, beginning with before you get out of bed do a BIG whole body stretch to help wake up your body, also in the evenings after activities take a very warm bath with Epsom Salts (an old curative) and then finish with your normal shower, but more importantly everything I have seen points to resting the legs well for 8+ hours nightly. 

However, if you have injured your knees during childhood you could have bone floating behind the knee cap and you could confirm this with an X-ray. 

Best of Luck Young Man, I will keep you lifted in prayer... a MoM in FLA.

Check out these websites for more information:

  http://www.ask.com/web?q=why+do+I+have+reoccuring+knee+pain&qsrc=2980&o=20036&l=dir

http://www.bigkneepain.com/

http://www.intelihealth.com/IH/ihtIH?d=dmtHealthAZ&c=290212&p=~br,IHW|~st,24479|~r,WSIHW000|~b,*|

http://www.netdoctor.co.uk/achesandpains/kneeinjuriescartilage.htm

http://www.nlm.nih.gov/medlineplus/ency/article/001258.htm

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