If your book is underperforming or not selling at all, and you are pouring money and effort into it, please stop for a minute.
Take a deep breath. Now, let's talk seriously. At some point you should make informed decision, should you continue or should you move on.
Please, took your book you thinking the most and go through the niche validation process. Don't tell yourself: "I did it before starting the book." Life are changing, niches changes. Make the decision with current data, not past effort, and let the numbers tell you whether to commit or move on.