I see. Then the best thing I can tell you is to try something new.
Either start something else that is wildly and completely different, even if it's just a page or so, to spice things up.
Or try something outside your field. If you like computers, try making your designs if they were for a videogame. If you write, try a light graphic novel in the same world as your project. If you like music, make a theme song for your project. Animations, live action, plushies, anything!. Expand your horizons and find the fun again.
But if that becomes a chore, which all of this can become, I often try to look back to the beginning, see where I've come from, find the roots of why I've even started. Look back at old designs, old projects, old anything. I like to remember where I've started to experience those feelings of creativity again.
In the end, anything we love can become a chore. We just have to think a bit, wonder why we do things. If it's all for naught, then why are we doing it? Personal gain? Personal fulfillment? Or, as I like to think, if I can make one person find some enjoyment, get some reaction, either a giggle or a sneer, they looked at my stuff and found an experience. If I can make one person smile through my work, then it's all worth it.