Not sure how to help you out with it, but you’re at least not alone. Robert Smith from The Cure had the same problem with the song “Friday I’m in Love”: https://en.m.wikipedia.org/wiki/Friday_I%27m_in_Love

“During the writing process, Robert Smith became convinced that he had inadvertently stolen the chord progression from somewhere, and this led him to a state of paranoia where he called everyone he could think of and played the song for them, asking if they had heard it before. None of them had, and Smith realised that the melody was indeed his.”

No, you see it’s: “dun-dun-dun-dudu-dun-dun dudu dun-dun-dun-dudu-dun-dun”

not

“dun-dun-dun-dudu-dun-dun, dun-dun-dun-dudu-dun-dun”

Nope, happens a lot to me, too. Worst part is that whatever you’re accidentally plagiarizing, will immediately sound great and will be really easy to write, because of course, you’ve listened to it before. And it can be nigh impossible to distinguish between accidental plagiarism and just being in a flow.

Everything is derivative of something else. Thag made that drumbeat on a rock 20000 years ago and it has passed down in oral history to eventually be in a Nirvana song.

This sometimes results in songs like Dani California that are almost certainly overt or unintentional copies of another song. When you find out your song is subjectively too close to another song you do the right thing, whatever that may be between you and the original musician.

Art is theft

All art is inspired by other art, it grows, evolves, eats itself, parodies life, informs living.

I wouldn’t worry about it

I simply don’t think about it. If Chino Moreno can get away with using the chorus chord progression of “Hit Me Baby” in one of his songs and the most that happens is laughter about it in the comment section, it’s not an issue.

Alternatively, there is nothing new under the sun. Music has seven fundamental notes that can only be arranged so many different ways and still sound pleasing to the ear. It’s an inevitability that somewhere, you’re going to use the same chord progressions as thousands if not hundreds of thousands of other composers, you’re gonna write the same licks, you’re gonna play the same riffs. The difference is in atmosphere, genre, and performance. Don’t stress it too much.

Don’t worry about it. There are only so many progressions. Everything else is just variations within them, with bass lines, melodies and rhythms.

Run it through shazam (or a foss alternative if there is one) and check?

I’ve done this. Yes, they did exist. That’s one of the risks of creating songs from melodies stuck in your head

You don’t. I used to write music, and I would frequently think I’m writing a melody only for it to turn out to be something I heard in the background of a TV show or something.

No you see, that’s the secret. All my songs are just me Weird Al-ing every aspect of them.

Eventually they’re different enough that they’re truly mine.

Copyright bullshit has made artists paranoid.

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It might be similar to a song you’ve heard but you’re misremembering the notes of the existing song.

Maybe try playing it for an app that recognizes the song that’s playing and then listen to any songs it guesses might be the song.

It’s normal.

Especially if you’re writing in a popular style, tons of musicians just use the same chord progressions over and over .

Once you start layering things on the melody, it’s pretty unlikely that it will resemble anything too closely.

As long long as you’re just using your own creativity, I think it’s very unlikely you’ll just clone a song.

If you’re really worried about it, you can just change a few notes in the melody on the page in a way that you wouldn’t think to sing “naturally”