They wont let me post a image.

Anyway, I'm 18. I just noticed on the very back of my head (but still on top) theres a nice X bald spot. I have no idea if its even hairloss, or just natural. But the hair is pretty thin back there so I am guessing hair loss.

Any idea on how I can regrow the hair, if it as at all possible?. Being bald (more then now) on the back of my head when I hit 23 is not something I want to look forward to.