I think it's really common. And there are two things you can do. First one is ask yourself what you can do to make your song better, a song you can be proud of. It's difficult, but it can be done. The second is to accept that it's not the song you wanted to write, and move on. Write something else. Even the best songwriters have ideas they don't like, half finished and abandoned songs. It's all part of the process; they make room for the good stuff.