You worry you are lacking some internal element necessary for writing anything that matters. I want you to know that, while this is a lonely suffering, you are not alone in experiencing it. Also, it can be survived.
"…I was so bogged down after so much time working in the dark that I saw the book foundering and did not know where the cracks were. The worst thing was that at this point in the writing no one could help me, because the fissures were not in the text but inside me, and only I had the eyes to see them and the heart to endure them.""