Hi Norman,
If you're feeling unhappy about your sales, want to do some problem solving?
Without knowing your work at all, I can think of many reasons why sales might be poor:
1) Bad reviews or not enough of them.
2) Books not being found due to no keywords or incorrect categorization.
3) Quality/Editing issues.
4) Weak book Descriptions
5) Too many titles unrelated to each other (genre hopping, someone may like one book but think your other titles are completely unrelated/different)
6) Extremely niche topic, without much readership.
7) Pricing is way out of the norm (too low/too high)
8) Poor cover design
As I've said, I don't know your work so I am not assuming that any of these are true. But it might be a starting place. Why do you think your sales are low?