Book Publishing Depression

When I finished my book at the end of NaNoWriMo last year I was incredibly excited. I was so proud of myself that I had finally, at long last, actually FINISHED a story and accomplished a goal. It may not seem like a big deal to you but to someone who is a chronic procrastinator and my own worst critic, it was incredibly satisfying to see that little screen saying that I had won. It was like being on a drug high. I was ecstatic! 

While still riding that high I decided to use my coupon from NaNo to get to free paperback copies of my book from CreateSpace. And that is how The Letters was published. Like a premature little baby that was exactly quite ready for this world, I pushed it out there anyway. I was so proud and top of the world that I thought surely someone will read it and like it. Then came the pep talks to myself of "Well, even if no one else ever buys it, I wrote and published a book, which is something I've always wanted to do so there's that." And there it was, indeed. 

I should have done more research beforehand instead of learning as a I go. I'm sure it would have made this process so much easier. But I didn't, and here we are and I'm not complaining because I've actually sold almost $100 worth of books and I had maybe $10 total invested in it? 

But.....here I sit, researching ways to market this book and promote it and feeling not necessarily discouraged but depressed. That's the only way I can describe it. My book has gotten several good reviews. And those reviews were from people who didn't even know me! I've started on a prequel to The Letters to introduce more back story of some of the main characters but I can't seem to stay focused on it. A part of me just doesn't want to write about those characters anymore. At least not right now. The high has worn off and my inner critic has come back and all I can think about are all the things I have done wrong when it comes to this book and publishing it. Not to mention that I'm really on the fence about Amazon and I'm sliding more and more to the side of wanting to tell Amazon to suck it. 

I just can't seem to get out of this funk where my book is concerned. I've got it on a few review sites. I've done some promotional pricing. I've done giveaways. I'm still researching how to do more but it just seems to depress me more. Don't get me wrong, I love The Letters and I'm proud of my writing. I'm just....in a funk? 

Has anyone else had these feelings of depression after putting out a book? Am I being weird or is this a writer thing? If it's a writer thing, how do you overcome it? And as a bonus, what are your thoughts on Kindle Unlimited?