You were luckier than you realize. I’m with an imprint of a fairly large publisher. I was responsible not only for writing my first novel, but editing, doing all the back cover copy, promotion, videos, cover design, etc. Yes, it’s a thrill to see one’s book on the shelves at Barnes and Noble, but it’s no guarantee future books will end up there. If your first doesn’t make the numbers in the initial six weeks, you’re on the way out. These things should have been explained to you before you reached the point of “barely breathing.” I also have to laugh at anyone saying they fired their agent. It’s a wonderful feeling to say “I’m going it on my own,” but you don’t get into bookstores if you’re not agented. I hope that was explained to you as well. Good luck, anyway. At least you made it to The Big Six. Most writers don’t.