How do you keep exercising, even though it’s hard and you don’t want to?

First off it’s undoubtedly hard but think about the reason(s) you started. and then start or restart small. You could start with 10 minutes a day and then build increase the it over time as your body starts to enjoy it and your start to feel more comfortable with it. It gets easier and more interesting and tolerable once you start seeing results.

The motivation comes from the feeling of success. You've probably completed a task that was lingering over your head and felt that proud feeling. When I have to get up and exercise, I imagine that feeling of success and how good it feels. Hopefully that helps.