Awww. First off, I'm sorry to hear you've gotten harsh reviews. They're always hard to swallow, especially when you don't feel confident.
But if it helps, reviews are something written by readers for readers - they're not typically something meant for the writers themselves. A story usually moves itself in its own trajectory. Most published works don't sway with the audience. This is because the authors who do so might lose the audience who actually like how the story is written and how it's going, since they'll end up swaying it to please one or two of the more vocal people. I'd suggest getting more reviews or comments first before deciding on what to change.
There are a few things internet self-published writers hit snags with, which we can also learn from. I'm not sure if your reviews mentioned them, but these are the two I can think of from the top of my head.
If we're constantly getting negative comments or reviews about our grammar, which is something a lot of authors seem to get, it's not a bad idea to look into editing our work or having proofreaders go through it. If you can't afford it, get a beta reader. I'm from the fanfiction world and folk in fandom pockets are pretty big on helping each other out by proofreading works before they're put out. If you write for a genre, even if it's original work, you can try looking for beta readers who want to help you improve, and offer them something as a trade - fanart you can draw for them, a story they can request from you, adding them as a character in your story, etc.
If you're consistently getting negative reviews about consistency with characterization, bestiary or the world, you can try keeping a log or project folder for each character, world, beast, etc. You won't be able to remember most things several chapters down the road, so keep it around to flip through it. Your outlines and your notes will be your best friend. Having notes will also help with pacing. You'll know how fast or how slow you're going if you have a "where am I right now" jotted down in a timeline you can see.
I know it's exciting to delve into just getting words out over an lovely idea we have, but spending time to study and look at tips as well as reading published books from a bookstore pays off in a lot of ways. Works put out by publishing houses often have a lot of editing and proofing done already, so they're a very, very good source to learn from. I'd also recommend reading the classics.
Don't be afraid to take a hiatus, buy hard cover classics and curl up with them in bed. In three to five weeks, you might find yourself writing very differently indeed. The reviewers who left those comments before dropping your work may not see the change, but folk still following you will.
You might leave them breathless and awed!
