I felt like this too sometimes, especially in college when I was tired from studying. One thing that really helped me break into more movement was linking something I liked to movement. For me, that was promising myself that if I watched another episode of a show I liked on Netflix, I would watch it while walking on the treadmill or on a stationary bike. I forgot I was even moving! And I got to stay in an air conditioned space.
Another thing that helped was a Fitbit. Having the step goal was a great motivator, and when I reached the goal, it felt like a big accomplishment.