Jim Butcher (of Dresden Files fame) once described the creative process. He said that, when writing a novel, the start of the novel was easy to write. And the end was easy to write. But he had the hardest time ever in the middle, to connect the beginning and ending which he saw clearly.
For our perspective on RPGs, it's probably the same. It's easy to start making an RPG, when the towns and concepts start easily. And, it's easy to visualize the end of your RPG, perhaps the climactic battle between the Final Boss and the PCs, and when the Dark Conspiracy is totally uncovered, and the world hangs in the balance.
But, the middle is always the hardest. You have a chunk of the RPG done, so you're confined in what you create, and yet you're also confined because you want to coherently steer the game towards the desired ending (or endings if your game has multiple endings)
I'd say see where the current threads in your RPG go. In my little example, maybe the start was pleasant, but now quests start to have hints of darkness or insanity, maybe PCs and NPCs have phases of doubt or other changes which lead them towards the ending.
And, as others have said, maybe you need a break from the RPG. After all, creativity does not come on a set schedule.