How to stay in shape while in school?

I feel like I struggle with this a lot. I feel as though all I have time for is studying, attending class, and going to work. I want to be healthier, I’m not overweight or anything but I want to add physical activity to my day for at least half an hour. I just feel like I get so tired all the time. If it helps I usually work 25 hours a week and I am in 4 class including 2 STEM classes that are on the heavier side for sure.