Perhaps you're just feeling overburdened or there's too much work.
This can happen, and sometimes it's just a constant , never-ending workload. It might be caused by you over-stressing yourself, or other related factors. There's plenty of people who're okay one day before , and then the next day they suddenly lack the motivation to do what they need to do. I think that perhaps, what you need to do is to relax, kick back and enjoy school. There's no point stressing out about things too much when you're still so young
Think of the world and it's blessings as discoveries you can make, and your everyday experiences a journey. The more you enjoy them, the better.
I think that what Ellie said is perfect.. you should join new activities, have something new to look forward to, and remember that nothing's beyond your reach
Another thing to remember is that though you might feel challenged at certain times, new activities lead to new inspirations , and new inspirations lead to happiness.
A change of mindset and how you look at things will certainly help.
Also, if you ever need someone to rant out to or just want a hug
or a friend, I'll always be around.
Remember, there's no reason not to get into fun experiences that will color your life with excitement and joy!