I think that's the nature of playing music, unfortunately. I found myself hitting plateaus that were lasting longer and longer. It's hard for me to say what you should do, because I don't know what you're into or where you are with music, but for me, learning more theory, as well as learning more about different kinds of music, have helped me to grow as a musician.
When I was younger, I mostly was into hard rock music. Then I started getting into more diverse stuff like 20th century classical, all kinds of weird experimental music, and old soul records. There's a wealth of amazing music out there, and listening to more of it will almost undoubtedly give you more ideas about composition. A lot of people get into jazz when they are stuck in a rut, but I would advise against that.
Another thing to consider is this: a lot of bass players mostly just pay attention to the bass player in music they like. I don't know if this is true for you, it's just something that I've noticed (and it's not exclusive to bass players, many musicians focus on their instrument). Even before I started composing music for instruments other than bass, I found that I could learn a lot from guitarists, drummers, cellists, and keyboard players that directly helped my bass playing. In fact, I woud say that at this point, my writing and bass playing are influenced more by drummers and guitarists than bass players.
Could you tell us more about what kind of music you play, how long you've been playing, describe your style of playing bass? It would help people know what they should recommend to you.
