Well since you metioned that this has been going on since your site has been up, I imagine you placed a link to your e-mail on your web page and now all the nasty spam-bots have spidered it. Try editing your email link to read: [email protected] and instruct anyone mailing you to remove the _NOSPAM from your adress, this will trick all the automated adress harvesters.
-Maestr0
