I went through th exact same thing but I was undiagnosed which made me think it was my own fault. If it’s hard to find the motivation in your current situation, try to think of the future you, the one already in sixth form/college, who’s applying to university. If you caved in to your lack of motivation and gave the bare minimum, would you be happy with that in 2 years time? I look back at myself in GCSEs and I wish I’d just stopped being so lazy and revised more! Sure, I did well, but I know I could have done way better! Use your GCSEs as an opportunity to test how far you can go. If you can push past the feelings caused by your anxiety and depression, you’ll be capable of amazing things which you’ll be really, really proud of in a year! I know this answer probably won’t help but just keep thinking of how happy you’ll be once you get the grades you want and how that feeling will last for a long time. What you feel right now in terms of lacking motivation will go away as soon as these exams are over so don’t let them limit you! Good luck!! I hope you do absolutely amazingly and make yourself proud.