I know exactly what you mean, so I'm just gonna give you some things that I did and if it helps, it helps.
1. Delete social media. This is the best thing for me personally. I understand it gets really hard for some people but honestly, after a few months of not having it, you don't even crave it anymore and shi just feels peaceful. I didn't delete snap cause that's some of my friends main way of communication, but I deactivated and deleted insta and tiktok- best decision ever. I'll deffo get it back after GCSEs but I feel so good w this I lwk might delete it in yr 12 asw
2. Pinterest. It's such a feel good motivation board for me, where everything you see is curated for what YOU want it to be. I constantly interact w those tiktoks where it's like them "toxic" motivation (they don't seem toxic at all but it motivates me nonetheless) so its all over my feed. Plus, I really wanna live in LA when I'm older, so I fill my feed w things like that asw so it's like a small reminder as to what i could do if I actually lock TF in.
3. This is probably the most helpful if the other two don't seem very applicable, but abuse TF out of the weekends. Try not to wake up too late or that already starts it out lazy, and immediately play some good music when you wake up. Like you're some main character or sumn, idk I like it. Do your morning routine- brush, breakfast, blah blah- and then sit down on a table and chair- NO BED- and grind. Pick a hard subject. Something you don't like or find hard or that you're behind on. And don't base it on the amount of time you study, instead, focus on the amount of topics you do. And no music w lyrics when studying memorising things (I can give you recommendations on what you can listen to that helps if you need). By the time you get to lunch, you'll feel like you at least accomplished something. But lunch is your break and we are not getting off that grind. Eat your lunch and talk to people. Your parents, siblings, anyone and anything. Not watching your phone or TV. Or read a book. Sumn. The second you're done eating, GET BACK ON THAT GRIND. Start a new subject after luch. Do the same until dinner, yada yada yada.
4. Plan. I have a small book, and in that I have left two or three pages. All dedicated to why I want my grades. Why I need the grades. Then, on a seperate page, I write the date, how many days until GCSEs, how I'm feeling and what I'm gonna do. A small checklist and it gives me a reality check.
But yeah. I'm no study freak or school topper, but these things definitely have given me even the tiniest bit of motivation, and I'd say that is better than none. Plus, ik I'm not 'not capable' of getting the grades I want. And neither are you. No one is if they REALLY want it and REALLY out their mind into it. So literally just remind yourself how much you want the grades and that'll be reflected in the effort you put in.