Productivity is not the same as motivation . It is impossible to stay motivated all the time, but that does not mean you cannot be always productive.
Difference between average and productive people is that average people always fear from failure and give up when it strikes. Productive people on the other hand actively seekout failure because they know success is on another side.
You cannot expect to be more productive overnight , you have to probably spend your cultivators on your work habits.
To do list often fail because we make them too complicate or in an unequal manner. Some task will take a long time , others won't take any time at all. This is the major mistake we often do while making to do list.
One of the easiest and most practical thing you can do is to breakdown your goals into several smaller goals.
Tracking your time even if no one is asking you , can help you understand your work habits and the time when you finish work most successfully. Tracking your time for some days will help you see where you spend your time and will help you better estimate your goals. You will also get to know your problem areas where you tend to be more or less productive.
Along with your work you should also focus on exercise. This is not only about staying in shape or losing weight but to keep yourself more productive because it increases your alertness. It increases your blood flow and cardiovascular health which helps you to be less anxious,more focused and more capable of dealing with stress.
Stay productive and remain focused.