You say, “self doubt.” What, exactly, is it that you “doubt?”
There is a common misconception that “art,” of any sort at all, “is ‘easy.’” Or, that it would be, “if only you were <<something that you think that you are not>>.” If only. If only. If only. “Bah!” 
“Creating something” is always an uncertain process in the sense that you don’t know exactly where you will wind up until you get there. But you should simply approach the process with that expectation. Make some step, forward or backward or sideways, every day.
Charles M. Schulz created 17,897 Peanuts comic strips, one at a time, by hand. He did it with self-discipline: every day at about the same time, sitting down with a little notepad and doodling. Focusing on that. Some days, no ideas would come. Some days, they came in a torrent. But that sacrosanct period of time, every day, was reserved for creating comic strips.
Another trick that I frequently use is to have a daily diary – literally, a loose-leaf notebook and a number-two pencil, which I call my “running log.” What I’m thinking about. If I don’t know how to do something, write it down. Thoughts. Plans. Anything at all. If I “doubt” something, I sit down and write in the running log: what I think the hold-up is, free-thinking of what I could do, and so on. All in pencil, all by hand. And, I never tear pages out; never throw them away.
For any project, I also try to project-manage myself: what is the timeline? What are the depenencies? How can I make the most efficient use of time and keep my options open? What is the task punch-list? And so on.
Creativity is a process. That process can be managed.
