I have recently started to invent a story that I hope to turn into a published novel. I'm still at the very beginning of the process though, I'm still not done sketching my plot. I sometimes have these gusts of inspiration that win me over and have me come up with a lot of ideas at once, but the big issue is that I can't help but think of a movie/novel that has already used that idea right after thinking about it. So with each idea I have, I start wondering whether I thought up the idea first and linked it to an existing work afterwards or whether it's the reverse. If it's the reverse, it makes me feel guilty for it pretty much means I copied an existing work and thus have no personal merit, doesn't it? And even when I thought of a certain idea before linking it to an existing work, I still feel discouraged because the fact that I knew of the existing work probably subconsciously brought me to that specific idea (hence the fact that I immediately link the two afterwards)... or something? I don't know... I feel so uncreative and dull for not being able to come up with plot elements that haven't been done before (love triangles, rebellion against the current powerholder, commitment fear when it comes to relationships, etc.) to the point that I often consider quitting writing my novel. But then again, is there really something that hasn't been done before? Should one feel guilty/be discouraged for failing to be original? Or does the writer who re-uses old ideas and makes something nice out of it have as much merit as the one who makes something nice out of something completely new?
As with most existential writer questions, reading is a cure-all. In this context, exploring the different literary movements throughout history and the authors and work that characterized them provides insights and answers about originality and what it means to be original as a contemporary writer. Is this your first major writing project? My advice is--surprise!--to take a break from the larger, novel-length project if it is tormenting you and work with other forms such as short story, flash fiction and essay. This has helped me to take steps toward finding my voice and my perceived place in a world full of aspiring writers, many with great talent and original ideas.
There is a famous saying, although I can never remember the exact wording or the exact number or even who said it originally, but the gist of it is that there are only a dozen or so stories to be told and EVERY story is just some variation on one of them. YOU are original. You will have something to say that's unique to you. You'll have characters who are unique, as long as they're characters you're creating and you're not trying to create some other character that you like. Put bits of yourself into your characters. They'll be more real that way and no one will have done it the way you do.
Welcome to the forum. Please read the forum rules, particularly about posting work for critique. Liz' comment about a dozen story ideas has been expressed with the number being as few as three. The number I've heard most often is seven. I forget what they are. It doesn't matter. I am currently writing a historical novel. Historicals have been done before. I've read some that were riveting. John Jakes wrote a whole series that was painful - pure formula writing schlock from beginning to end. But no two historicals that I've read were alike (well, except possibly the individual volumes of Jakes'). Some of what I am doing has been done before. But it hasn't been done in the way I'm doing it, with the collection of characters I have. More importantly, while you may be dreaming of publishing triumphs and movie rights and Pulitzers, the fact is this is your first major writing project. You'll be far better served if you simply give it your best and understand that it is, first and foremost, a learning experience. We all learn (or should do) from our first attempts at a novel. For example, I learned that 400,000 words is waaaaaaaayyyy too long for a first novel. So, enough already. Go. Write. Learn. Grow.
Your novel idea does not have to be original. There are virtually no truly original novels published - there aren't many basic plots and they've all been used before, going back to ancient times and mythology. The originality you will provide is in your approach to the material - who your characters are, your personal worldview, your style. Don't worry too much about forcing these things, either; as you learn to write, you'll find your originality magically bleeding into your manuscript, whether you're conscious of it or not. Look around this forum. You'll find this issue discussed endlessly in older threads. BTW, welcome! Read the rules, look around, and participate!
You just have to keep trying, until one of your ideas impresses you so much that you don't care about any of that, you can't bear not to write it. Writing is a struggle, but in the end, it's worth it. As many here have said, there's no such thing as 'original novel'. Because there's no such thing as 'original experience' (or it's very rare and ultimately, derivative). But there is such a thing as your story. That is unique and worth pursuing. In my experience, it takes a while to get to that story, until then, keep practising.
I've heard someone say that there is only one basic story, with two possible endings. A person is looking for something. In a regular story, they find it. In a literary story, they don't. It's surprising how many books and films can be reduced to this formula. I wouldn't worry too much about your work being original. Everything has been done in some form before, but that's not a reason not to do it again, and differently, and better. Some of the best work you do will likely be inspired by other things you have read, but this is a good thing, something to be embraced. Art is, after all, theft. I found the book "Steal Like An Artist" to be particularly helpful in its discussion of inspiration / copying.
Originality happens often in writing. If you tasked a hundred people to, in less than a hundred words describe a picture, none of their descriptions would match (a few might). All descriptions of the same picture, but all slightly different. While you may not be totally original, you can still show your originality on a take of a similar tale. Just try not to copy someone else's work. When you reduce elements down enough, every story sounds the same.
There is nothing new. Life repeats itself until it phases itself out. People still tell stories and will until the end of time. That's our survival. You are at a crowded party and 5 people tell a story about the train wreck they saw on their way over. Each will have his own version, each will have his own degree of animation and verbiage and you will listen intently to each one because it's a train wreck for crying out loud! But they're all telling the same story. So when it's your turn, you tell the story so that all the partiers put down their beers and their smokes and stop making out and turn and listen to your story. That's what makes it new. You.