Hey- what you are describing is a feeling that we all have had. It is damn-near impossible to guage one's own progress. There is no way that we can be objective about how we are progressing; It is a lot more evident to those around you than it is to yourself. My recommendation is to stop worrying about that aspect of it, I think its a drain on one's energies. Instead, try to get some fun out of it, try to remember what first propelled you toward studying the bass. Make sure that you are engaged in as many musical enterprises as you can. In other words, play your bass in as many settings as possible. Its difficult to feel stagnant if you are constantly receiving stimulation from other musicians.
Lastly, take time to listen, find something new to listen to- a different style pf muisc, or a different artist. Sometimes that can be the kind of inspiration you need. Above all, don't despair over it- these sorts of artistic struggles sort of go with the territory. Best of luck-
JS