To write, is something every author does from the heart, whether it is a factual or a fictional book.
On days words will flow and you will find the ease of writing a pure joy as the hours fly past and the words, as if by magic, appear on your screen or sheet of paper.
At other times the opposite can be true, writers block - I can see you nodding wisely - or maybe it is just the thought of attaining the unrealistic target you have set yourself. Afterall writing is an artistic emotion which is not governed by hard nosed deadlines.
A middle way is often the best means of achieving a steady and worthy flow towards the satisfying conclusion of your article or book.
So, deep breath, let go the battle and take solace in quality being far better than quantity, maybe remember the Hare and the Tortoise.