You gotta not doubt it
Writing is only one of the tasks of writing, the other is believing that you can and should and have something worthwhile to say.
Should you do a writing course? (and what if you can't)
I mean, if you can, amazing. But if you can't, here's some suggestions.
Writing hack to defeat the doubt (aka, write to an audience of one)
How do you stay engaged when the process isn't fun? How do you keep the faith when you feel like everything you write is shit?