If you’re to the level that you’re playing, say, a half-dozen or so songs from memory here’s a little something that will build up your “music muscles”… write your own song.
So what if it’s not destined to be #1 with a bullet?!
There was a guy who used to show up at open mikes around here who’d written a song for his dog. The chorus consisted of him singing “Good doggy!” over and over again. His dog, who was always there with him, lapped it up.
You can just start with chords from another song you know and play about with them until you get a good sounding progression. Add some, drop some, change the timing a bit so you won’t end up just writing different words to someone else’s tune.
Blues progressions are nice to start with too. They’re mostly simple and there are types of blues where it doesn’t matter that you’re singing different words to an “old classic.”
Start humming along, pretty soon you’ll have a melody line that sounds good with your progression (and one that you can sing!).
Now write some words. Remember, they don’t have to be deathless gems of beauty and truth. Nor does this have to be an aria-length opus. Tons of great tunes out there that are 3 minutes or less. Her Majesty by the Beatles is less than a minute!
There’s a ton of info on the web about songwriting, traditional song forms, etc. that you can learn from if you decide you like this songwriting thing and want to do more.
But for now go and play your song for somebody. Even if it is just your dog.