Motivation is easy*, that's just doing what you want/ avoiding what you don't want. Not getting destroyed by a threat is pretty good motivation.

Discipline is a skill that you have to learn and practice. It's all about doing the things you don't want to do. That's hard when your primary motivators have historically been "don't die, don't get attacked, don't be poor, don't live on the street" etc, stuff like that.

You said you give things up after a month (presumably when you lose motivation)? Make it last 6 weeks. You don't start tasks until 2 weeks out? Make yourself start 3 weeks out.

Build the skill. Train it like a muscle. Start earlier, stay longer, push harder.

And give it time; progress is incremental not instant. If you're already succeeding, that's a pretty good foundation to start from. Now just get better at it.

*I don't mean getting motivated is easy, I just mean it's easy to do the things we want to do when we want to do them.