I've also felt unmotivated to do things I ostensibly WANT to do, and it's made worse by a sense of guilt that comes with not doing the thing -- like following through on my wishes is a duty, and if I fail to do so I've let someone down. Not a great feeling. Depending on the task, there's a couple things I've done that have helped:

1. Accept that what you're doing is hard, and adjust yourself accordingly. When I struggled with a lengthy writing project for a long time, I eventually had to accept that I wasn't capable of organizing something so big on the fly, so I took a step back and focused on taking notes with the goal of making an outline for the book. I've tried picking up books of philosophy that make my head hurt, and after realizing I wouldn't be able to understand it on my own I sought out what other people had to say about the book to see if their commentary could help me. Homestuck's a fun story, but it's also very long, very dense, and very complicated -- among other things. If by some chance your lack of motivation comes from an aspect of the story you struggle with, it's possible to find a work around. Listening to a Let's Read like Nexus (or Brodemus, my personal fav) can make the work of getting through long stretches of text easier. And you can look up meta or ask questions to other readers if you ever get lost. Reading is fun but it's also work? So don't worry about seeking help when you get tired. (Ofc ignore all of this if it has nothing to do with your problem)

2. Find something to do offline. It's cliche but it really is nice to take a break from the social media world. I like going to karaoke on the weekends and singing my lungs out, or I might take a long walk by the river. Sometimes I even make a point of leaving my phone at home so I'm forced to latch onto something else in my idle moments... idk. Resisting the urge to doom scroll is legitimately difficult (the websites are huge because they're very engaging!) so sometimes you need a good distraction or a physical barrier to enforce your vacation.

3. Take a nap. Sometimes I'm tired of doing stuff because I'm physically tired, and "physical" includes my brain. If you're tired beyond the stuff you described (since I imagine you have a bunch of school stuff to worry about too), you might just need to rest more -- take a nap! You might wake up with more energy for the things you want to do. (There are other causes for chronic fatigue ofc, but ideally you would have one that's easy to deal with lol)

That's about all I have off the top of my head. Hope it helps