Before and After the Book Deal by Courtney Maum
Before and After the Book Deal: A Writer's Guide to Finishing, Publishing, Promoting, and Surviving Your First Book is a fantastic book that lays out everything an emerging author needs to know about the publishing industry. Though I'm still in the querying phase of my debut novel, I found the "After" section extremely helpful. I thought I knew the ins and out of the publishing process, and how postpublication worked, but it turned out there was a lot I wasn't privy to.
Whether you're an aspiring writer or already have a publication or two under your belt, you need to read this book! It's full of resources and information and provides words of wisdom from numerous authors who have been through what you're feeling.