It's extremely common for writers to read or watch something and feel inspired to create an original story. You just had an intermediate step.
You're asking me about how, but my questions back to you are about why. If you can grab hold of why you're focusing on writing original fiction and confirm that you really do want to be doing it, a lot of these pieces will fall into place.
You're not entirely starting from scratch—many of your skills will carry over—but skills aren't methods, and you will have to develop new methods.
What's depleting you isn't the act of writing; it's the shame you feel about how and what you're writing.
What makes an original work original isn't that it exists in a vacuum, because no work exists in a vacuum. It's that you layer originality in with the elements that respond to the canon, the genre, and the world.