Not so Original, Original idea?

I have this problem where I find there is no such thing as an original idea. Or, if you do have an original idea, as though there is a chip in your mind a few years later someone comes along and you see your idea spread out for all to see. Problem? You didn't get any of the credit it! Writing seems to be a medium where this happens a lot for authors.

I can't even tell you the amount of times this has happened to me and it's starting to become a running joke, to the point where I don't even bother telling people my ideas anymore because on some strange unconscious level there is a paranoia that just speaking it will ensure it's stolen. Serious crazy town set up going on in the mind, but what then do we classify as an original idea? How do we protect our mind from penetration. Not literally of course, after all Inception is not real...right?

As a writer and aspiring novelist my biggest fear is being just another book on the shelf. I have already, once had to completely rework my novel because a TV show emerged baring a frighteningly exact same storyline and character layout more or less. Ironically the story line was, loosely based on a series of books I'd never even heard of let alone read (though strangely enough the show was not much like the show or so I'm told). So, my exciting story became the victim of my frustration as I tore apart the foundations and completely reworked the idea. 

It still had similar basis as far as amount of characters and what they were because that was just a fundamental part of the story I could not, and would not change. It did however turn to work in a surprising idea I had not expected to work out at all and completely turned the direction of my story entirely backward. Though I am inspired and interested by the turn which my story has taken it is proving to be a lot more work in research and back reading. This original idea is not so original in the fact that it is drawing from and alluding to mythology and literary works of Irish pagan culture and folklore. So I have now a possibly original (who really knows at this point stay the hell away from my mind!) idea, filled with inspiration from my heritage and culture.

Is my story then unoriginal? Or is it still original? Where is the line and what defines it and how on earth are we supposed to create an original idea in a work full of creative minds and centuries of published ideas and stories. At what point as we drawing literary allusion and just plain old copying?