Hi,
I'm really sorry you feel like this, depression and anxiety is awful and I really know how you feel,
I live in the UK so we have a different system as it seems you do.
but I also suffer from depression, and my grades began to fall as I had no strength to study hard and go to all of my classes, I refrained from telling my parents because I felt they wouldn't understand.
I'll tell you what I did, and hopefully this will help
I spoke to my tutor, (so you have a teacher who you can talk to?)
I explained EVERYTHING, about how I was struggling and suffering from bipolar depression but was still dedicated to doing well.
doing this and sharing my problems made me feel 100 times better, I had someone to confide in and it took away some of my anxiety.
all of your problems CAN affect your studies, so the sooner you talk to your teachers the sooner things - with help - can get back on track.
you can't do this alone so please please confide in someone. You can always email me if you think it will help?
I'm not going to tell you to go to therapy, or get melds because in my own experience I found this didn't help me personally, but maybe it's something to think about and you can decide if you think this will be the way you want to solve your problems.
One thing that a lot have research has found helped is exercise, if you're anything like me - now sporty at all! - this probably sounds like your worst nightmare, but even just 10 Min's a day gives positive hormones - sorry i don't know exactly - giving you a good feeling! maybe try this?
I hope this helps and I really hope you get better, but don't let this rule you and don't suffer alone! You are not alone and if you look at all of the answers on here, you can see people care.
Lisa x x