As somebody who has suffered basically the exact same thing, one book that has immensely helped is: https://www.amazon.com/Self-Directed-Behavior-Self-Modificat...

Essentially I found that I could tackle any task, but on the first flash of some other more exciting idea, feeling or sensation, I would drift off.

The book boils doing to finding your own Antecedents that Lead to Particular Behaviors that you want to change.

A book that I have found very useful for both developing new habits and breaking existing unproductive habits is "Self-Directed Behavior" by Watson & Tharp. It's based on scientific research, but the ideas are presented clearly and in a practically useful way. It's also about more than just the introduction or changing of habits - it also helps you analyze them, understand them, measure them, reinforce them, etc.

It appears to be sold as a college textbook so the latest edition is horrendously expensive, but this also means you can easily find used copies of older editions. Mine is at least 15 years old and still very useful.

https://www.amazon.com/Self-Directed-Behavior-Self-Modificat...