John Lennon was asked, “What do you write songs about?”
And he answered, “Whatever annoys you.” (From what I’ve read, John probably used a stronger word than “annoy.”)
I recommend checking in on Corey Stewart Songwriting Tips regularly. A recent posting there says, “To be a songwriter you need to have the mindset of one. Always be on the lookout for an idea.”
You can check out some methods of determining the subject of your next song, and how to always have a “next song.”
WADE