Virginia Woolf said “The creative power which bubbles so pleasantly in the beginning . . . quiets down after a time, and one goes on more steadily. Doubts creep in. Then one becomes resigned. Determination not to give in, and the sense of an impending shape keeps one at it more than anything.”
If you’re in the situation Woolf describes, consider Write or Die. I’ve found it an incredibly effective way to get words drafted and highly recommend it.