"Some Days Are Diamonds, Some Days Are Rocks" as Tom Petty says....

Write something, anything....

Guess what, some days you simply may not have something to say! Great songs come from truly having something to say, however big or small. Think about how direct and impactful you are when you really feel something. For example, when you're angry you don't mince words do you? You're not searching for something to say, you just say it. "That is the last time you make a fool outta me, you g-d damn son of a..." you get it. How bout when you're sad, " The thing is, you were the only one who really 'got me' ".  all of a sudden you're confident and poetic and direct all in one.
When you don't have something to say and there just isn't a fire in your belly. I say, Don't sweat it. It's ok.
My suggestion is to write a song if just for the exercise.
Think of it this way, If a robber breaks into your house and you've been sitting on the couch watching tv and eating for the past few weeks you're not gonna have the muscle or energy to defend yourself. If you've been to the gym every other day, you will.
If inpsiration hits and you haven't written anything for a while, your writing skills are gonna be sloppy and not well oiled. You won't be prepared to capture the idea that just came to you. And that is the worst feeling in the world for a writer.
Simple put, a builder builds...a teacher teaches...a writer writes. Stop thinking and start writing. Guess what? I wound up buying a house from a song I wrote on a day when I didn't think I had something to say.