Keeping going
Cues and friction
Habits run on the situation around you more than on willpower.
Much of what we repeat is set off by cues: a place, a time of day, the thing we just did. Once a habit forms, the cue can start it with little thought.
That's why the situation is the easiest thing to change. Put the book on the pillow, the shoes by the door, the phone in another room. Making the good action a little easier and the other one a little harder adds up.
Try this
Tie your promise to something you already do every day: "after I brush my teeth, I …".
Sources
Proposed that habits are triggered by context cues, often independent of a person's current goals.
Wood, W., & Neal, D. T. (2007). A new look at habits and the habit–goal interface. Psychological Review, 114(4), 843–863.
Reviewed evidence that habits are cued by context, and that changing the context is an effective way to change them.
Wood, W., & Rünger, D. (2016). Psychology of habit. Annual Review of Psychology, 67, 289–314.
A general finding about how people tend to work — not advice for your situation, and not a diagnosis.