Check out that link to the wiki article that BigGoronSword posted. Check out the advice it has there; examine yourself in the shower every now and then for any changes in your testicles (the wiki article has some of the symptoms you could find, such as lumps or hardness on one testicle). If you find anything unusual, get down to the doctor and get it checked out.

If it's really bothering you, I think it would do you good to go and get checked out by your GP anway. Getting the all-clear will give you peace of mind. I don't think there's too much to worry about at your age though. Ultimately, it's better to be safe than sorry, so a quick check-up with your GP won't hurt.

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