It depends first of all on your definition of 'original.' You could argue that originality in pop music has been pretty much dead since hip hop arrived (and ironically enough, that was a genre built on sampling). On the other hand, you could say the likes of Bjork or Radiohead are always and deliberately 'original' - whatever that means to you.
But I think there's a fine line to be walked between a desire to avoid plagiarism (healthy and necessary to a point), and being so mindful of how your song compares to other songs that you can't focus on the job at hand: writing the damn thing.
I had a plagiarism crisis while writing a melody just a couple of weeks ago. I found a really nice tune, and thought to myself, hang on a minute - I KNOW THIS TUNE. And it rattled around my head, but I couldn't figure out what it was. I was ready to abandon the song, convinced I'd ripped it off, when suddenly it came to me. I knew what song I'd 'ripped off'. So I looked it up on youtube to confirm, and actually my song sounded nothing like the song I thought I'd ripped off - it simply shared a harmonic change and a held note, and so had a similar feel. I'm also slightly embarrassed to admit the song turned out to be 'keeping the dream alive' by Freiheit.... :/
If the fear of plagiarism is really bothering you, it may help to widen your listening material. Spend some time delving into artists you don't normally listen to, or discover something new that you really love. I find having a varied listening palate can help you move further away from your primary influences as time goes by. When I first began writing songs, they all sounded like I was trying to copy Neil Finn (mainly because I was!) but even though that's still a noticeable influence in some of my songs, they're nowhere near plagiarism (I hope).
One last really important thing: don't forget to have fun!