Dunno if this will help shake anything loose, but -
When I was doing the Beatles project, Neal Aspinall once remarked that the lads made an important breakthrough when they realized a song didn't have to be songwriter-centric (as in "I'm in love, I'm so sad right now, I like to drive my cool car really fast" etc.)
They started writing songs that were directed toward other people - She Loves You, You're Gonna Lose That Girl.... At the time, this was pretty unusual in pop songs.
They kept heading that way, next thing ya know they're just outright telling stories about people. Ob-La-Di, Ob-La-Da, Eleanor Rigby, Rocky Racoon...
So... if you can't think of anything to say about yourself, is there something you'd say TO someone? Or maybe there's someone else's story that needs telling?
Just a tip from the Beatles.
EDIT: For example, I'd like to hear a song that starts with: Hey, kid - get outa the street
EDIT2: Also:
In the case of a musical, you're writing someone else's words, and you know what they're supposed to say.
Randy Newman made quite a career writing songs from the POV of characters he made up just for each song. In real life he doesn't actually hate short people and he doesn't particularly love L.A.