Discipline isn’t about being strict with yourself. It’s keeping a promise to the person you said you’d be.

Discipline usually gets pictured as severity, which makes it sound like a war against yourself that the strict side wins. A better description is contractual. You decided who you wanted to be, you said so, and discipline is turning up for that agreement on the days when the mood has gone. The person on the other end of the promise is you, later on.

Make one promise small enough to keep without willpower. Twenty minutes, three days a week, written down. Keep it on a day you do not feel like it and see what that does.