Maybe it's time for a break? If school is taking up a lot of thought space, it's okay to spend some time being mush and just recovering. You might find some ideas pop up when you let your mind rest.
Otherwise some stuff I do when I'm just trying to get my creative mojo flowing are things like thinking about my own version of fairy tales (it's easier to think about because there's already a framework there), or sometimes I think about pulling ideas from media I like, don't like, whatever I can think of. I will also retread old stories and reuse the same premise. This is all stuff I just do in my head, not necessarily for any creative projects.
Something else you can try are writing prompts! Especially super random ones. Do some low pressure for fun writing.
But overall, just don't be afraid to take a break! If you have an ongoing project, take a week or two off. If you have a lot going on in school, let that be your focus for a bit.