I know what you mean, motivation doesnt work for me. It tends to come and go on its own without any rhyme or reason or control on my part. Try rewards. I reward myself when I'm completely unmotivated. Also, give yourself a break. I tend to slip all the time. The trick is to get back up and get back into the good routines asap. Dont waste time beating yourself up. The sooner you just get back up, the sooner you can get into the good routine. Also, when I'm falling, it happens gradually. It's not like one day I'm doing great and the next I'm doing terrible. It's a cycle. Learn your cycle. Write it down. Pay attention. When you start to see yourself slipping, get yourself back on track.
Motivation. Keep thinking about why you don't want to go back to your bad routines and what would happen if you did. Know that if you did go back to your bad one, all of the progress you have made will be a waste.
Everyone tells me motivation...motivation...think about this and that. It doesn't work for me.