I've also suffered from the same problem. I'm very interested in my project and motivated to do it but some days I just can't. I've found one thing that can c

I've also suffered from the same problem. I'm very interested in my project and motivated to do it but some days I just can't. I've found one thing that can change my day from zero productivity to 100% is a todo list. I just write down on a piece of paper some tasks I want to get done that day and usually I've crossed them all out by lunch time. Of course then you'll procrastinate from writing todo lists but that's another issue. If you try todo lists, exercise, motivational books, etc. and still can't seem to focus on something you should be able to focus on, go talk to your doctor.