Reading a unit or and entire book comes from interest and placing the gains of reading it above anything else.To always get self motivated it always good to think about what you will gain from reading the unit and the book. When I don't feel like reading a book I tell myself I will be missing some knowledge I would have gain from reading such a book or I will be missing the lesson herein etc, you know most times motivations come when we placed what we would gain from a thing before us,it always helps put a spring on your heels to move faster.So placed your interest and what you will stand to gain when you read that units of the book in your mind or write them out and always remind yourself of the gains, it will continually help to push you to read.