Self-doubt is common.
I'm reminded of that story of the boy violinist. Skip if you've heard this one.
Little boy plays his violin for a world-class violinist. The violinist, after hearing the boy, grumbles a bit to himself and says, "You don't have the fire."
The boy, disheartened, puts away his violin and moves on to business. He becomes a successful businessman and, years later, meets up with the old violinist.
"I played for you once as a boy," he said. "You told me I didn't have the fire. I guess that was good advice, because I've gone on to do great things with my life."
"I didn't even hear you play," the violinist said. "I tell everyone that."
"What? But I could have been a great violinist! Why did you tell me that?"
"If you had the fire, it wouldn't have mattered what I said."
Do with that what you will. I say, keep writing. First drafts always suck.