I feel that way all the time, which is one of the reasons I don't write very often, haha. That, and no patience, but this is my advice.
Unoriginal stories with some "twists" and "tweaks" are still, well, unoriginal. At the same time, good luck coming up with anything that hasn't already been done in some way (not impossible, but very easy either). You can always follow some formulaic story, wizard takes a princess hostage, and some young person steps up to go find her. That gives you a frame, without any detail whatsoever, which is what's going to make your story. If you've got kickass writing and kickass characters, no one's gonna care if the idea's been done before, because you still wrote something worth reading.
Try to take what you want to "rip off," and cast it in a new light. Create a situation that's similar, but not so much that it's obvious where you got it from. Say you have a family of trolls or something in a story that come into town, massacre people, and steal a little girl. In your story, you could change it to be a warring state who invaded, introduced disease to the livestock, and stole some artifact (which I'm sure have probably been done before, ironically haha). But the idea is, you can take something you like and change it enough such that it doesn't seem like you're ripping anyone off, and you have plenty of leg room to make the situation what you want it to be to make your story unique.
That's "not very easy either," I meant
Another good trick I've found is to create a large pool of reference material and work to artfully combine them into something familiar yet new. The final result is clearly inspired by X, Y and Z, but it's also become its own animal.
Granted, the success of this technique has a lot to do with the talent of the writer and their ability to blend separate storylines/elements into something intelligible.
Like a horse and a eagle and a rhino? makes a flying Unicorn?
There are few things here that you're citing as negatives that can be spun into positives. If you are writing a story that seems to be very close to an existing world, or a body of another author's work, why not just make it a fan fiction type of work? This satisfies the fans as the world they love is being expanded, it allows you to use elements that fans are familiar with, and it does a lot of the setting work for you (which reduces the amount of work you need to put into making it immersive).
Alternatively, if you want something that's entirely your own but you like a certain genre, there's nothing wrong with making it similar to something existing. The way to really shine in this situation is simply to change a few things so that the world itself (or the characters, but I find altering the setting to be easier usually) has a few notable differences. Then you incorporate those changes into the story so that the storyline has to account for the changes, or the differences figure prominantly in such a way that the story focuses on the unique elements you're introduced while allowing the "rest" of the setting to be generic sword and sorcery!
Any way you choose to handle it, remember that unless you're trying to copy someone else's work, the writing style and the imagrey will be yours. To an outside reader, I doubt we would notice if a city seems a little too much like some other city from a book we may or may not have read.
Bro, at one point I was writing a story about a necromancer stealing corpses from graveyards and becoming a lich... how do you think I feel?
Honestly though, I just don't care. In my example I PMd Endmaster telling him about the situation and he was cool with it, after all there's not much else you can do with that archetype, so I would advise doing that if you're ripping off anyone around here. What I would suggest is just write your own thing, and if it sounds a little like somehting you've seen or heard or read before, that's common. Although we don't mean to plagurize (no idea how to spell that), what we read and enjoy influences us, and that includes our style of writing. So just do your own thing for now, and I'm sure it'll all turn out alright.
But if you have a dude named Hairy running around with Rod and Herboine and getting place into the Chimerador house after the Sorting Beret sees his inner self, I'm gonna call BS.