Something that always works for me is getting something that I really want, like a snack or a game, and say I can't have it until I'm done, a common problem with this one is that some people eat the snack before finished, myself included, so you could try to have someone else make sure you don't have it early.
If you experience burnout, what I do is for every 60 minutes I work, I take a break for 20–30 minutes. Remember, what you're focusing on isn't the only thing that matters. I recommend starting work on whatever it is as early as possible so you have more time to take a break later on.
I understand. I feel this too, as does almost everyone. But just remember, what matters isn't if you fail, but if you were trying to fail. After all, EVERYTHING that has ever happened, happened because someone had the will to try.
This is completely reasonable to feel, what I like to do to solve this is to work on the new stuff before trying to work on the new older, that way new work doesn't just pile untill it feels impossible