Criticism is something, as a writer, you need to get used to. It comes with the territory. There is no way around it. Even the absolute best writer in the world had critics. The challenge is this: do you listen to them?
Better yet, who are these people who are criticizing you?
Are these people jealous that you did something (wrote a book and self-published it, even putting it on Amazon for free) that they couldn't? Do their opinions really matter to you?
Chances are, many of these people will either be complete strangers or part of your family. Complete strangers don't have any interest in your success, so why listen to them? Family members who haven't achieved more than a huge pile of debt and no retirement savings to show for it are not ones to listen to either.
Then who do you listen to?
That's a good question. I don't really have much of an answer. You might want to listen to your agent or editor. Or even members of your writers group. Mostly, it could be your spouse--that's the one I lean more than anything.
Trust that inner voice and do what is right in your heart, not what others will think of you. The world needs it, if your heart is true.