The problems lay in the middle of the book, where I moved scenes around so often that I couldn't remember what was where any more. (and of course, every time I moved a scene, it and everything after it had to be re-written. Again. And again.)
So how did I solve the problem?
I cleared my pinboard of all those cute cat pictures and inspirational quotes, and created a note for each scene. Then I stuck the notes up on the board, in the order I'd slotted them into the book. Each time I moved a scene, or changed the chronology, all I had to do was shift little pieces of paper around.
You know that maxim that it takes a lot of work to make something look easy? Now I understand!
Never again will I under-estimate the work an author puts into a book that appears seamless to the reader. Because now I know that the author probably spent weeks wondering what was going on in her own story, how she'd managed to get the days backwards, and whatever happened to that scene...?
PS: Happy Valentine's Day everyone!!