I think whether you find your subject or not, you are doing exactly what you should be doing: struggling to find your subject! The issues of different formats, and carrying a notebook, and going w/out your camera, etc. are just exercises in an attempt to find one thing: the thing you care enough about to photograph it (for now anyway).
The talk about freeing the mind and focusing on what's important to you is right on point, I think. You might just step back and consider what's important to you as a person (not as a photographer), make a list of the first 3 or 10 or 50 things that you really care about, and then find one that's accessible AND that is visual. And then go make 10 to 25 excellent photos of it. This is the basic advice from "On Being A Photographer" by Hurn and Jay. Great book, you might get it and read the section on "Finding your Subject." I think it will help in your process.
But I hope you'll consider that, as an artist or as a photographer whatever you call yourself, you're exactly where you should be: working through what you want to show with your camera. The failed experiments are necessary steps in that process. Like printing, the garbage can is your friend. Same is true of shooting: chuck everything except what truly moves you. Sooner or later you'll find it. Then lose it. Then find it again?
I feel like I will always be in the process of discovering what I care about visually and photographically, and that when a photographer stops asking that question, his or her work slows down and maybe croaks.