Wierd penis fluid.

Sometimes, when a man becomes aroused, his penis will weap with "pre-com", a watery fluid that prepares the ureathra for the eventual passage of sperm.

This usually happens with levels of high arousal, but it could also happen if you have not experienced an orgasm or ejaculation within about two weeks... this normally happens after puberty, but as we don't know if you have passed into of through puberty yet, it is hard to say.

It may also be that you are about to become mature and start these sorts of "noturnal emissions" or "wet dreams" but haven't yet...and so, your body is primed and ready, and the excess sperm or semen is begining to leak with any sort of arousal, compression or exercise.

I wouldn't worry about it unless you have pain or the fluid smells.  These would be a sign of an infection.