This is an interesting topic I think applies to anything creative

Not that I'm the best author of creativity, but I had the same questions and have learned since then.

But my opinions on it are:
Creativity, or in this sense, music is emotionally driven, intellectually steered.

You learn what you like, you practice it, you sing along with it, disect it. Practice, practice, practice, experience, learn, etc. The intellectual part

But Spit out your emotions, don't worry about how nice it sounds, or if you're in tune, or what chords and notes your playing, or if your voice sounds like sea gulls, just let the emotions drive. Your head (the things you've learned in the past -that you like-) will eventually bleed out and steer for you in a direction that you like.

If you find yourself thinking too much about it, you'll go stale. Just pick up the guitar and play that thing and belch it out. Who cares if its "nuhhh nhhhh hmmm nuhh", let it rip, intellectualize about it later and fix the edges.

In fact, if you got words, and you got a chord/rythm structure, this combining of two different worlds will produce creative results. Just go for it, start singing the words out as if randomly. You'll find through each pass of the song as you practice will shape and mold how you will sing and more and more emotion will come out.

Music, creativity, its always unknown, you can't just learn to be creative. Enjoy it. It goes on forever there is no end to creativity that is the beauty of it. I think too many people look for popularity through creativity then they do to just enjoy it for themselves.

Not saying you're not doing this already, just my thoughts