Looking for a story

Hi all, I'm hoping someone out there will remember a story I read quite a while ago.

Here's the basic synopsis that I can remember:
I young boy (somewhere between 12 & 16) gets kicked in the groin by a bully (or it may even be a sport injury) but doesn't tell anybody, after a while he finally tells his parents about it because he's still in pain, on examination parents or doc's (can't remember which) they discover that his genitals are changing from MtF all on there own.

That's it, All I can remember, Anyone have any idea what it is called/who it's by?

Cheers n' Huggles
Sammi