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."