I am 16 years old and about 3 weeks ago discovered a lump at the top of my testicle, about 1cm long and quite hard and smooth. Is this my epididymis or could it be something more serious?

Here is a link to a drawing that I made of the general shape and size: http://img147.imageshack.us/img147/4199/32 695615ct0.jpg

Thanks for any help you can give. And btw, there are no other symptoms.