When I write songs, the lyrics are usually the greatest stumbling block. The vocal melody tends to fall into place pretty easily. Now I'm working on a song where the lyrics are almost writing themselves, but I don't like the melody. It's serviceable, that's about it.
So I should just think of something better, right? Problem is, I can't seem to get the merely serviceable melody out of my head to make room for something else. Every time I try something new, it morphs into what I had before.
The original melody may start to grow on me before I think of a new one.