It's OK to take a break. Being overworked is in no way your fault, and you deserve time to rest. It's only human.
No feeling is invalid. Feelings are natural, and you have barely any control over them. Take a deep breath, acknowledge what you feel, and decide what your actions will be. Your initial feelings don't reflect anything about your character.
Not knowing all the answers is perfectly acceptable. Arguably, it is the constant human state to not know the answer. The world is full of mysteries, both light and dark, and it is meant to be explored, not discovered.
You are your own person, and you have your own life. Parents, teachers, society, or books don't know what you want. Only you do.
Your grades don't reflect your character or your intelligence. It's impossible for your worth to be defined by the things you write on a slip of paper that get sent off to be graded by a human who inherently has their own biases.
It's OK to acknowledge that it's bad right now. It's good to know that it'll get better in the future, but right now, it's not, and that is valid.
Opening up to someone is an act of bravery. It does not make you intrusive, weak, needy, or annoying. Find those who are willing to listen and talk without guilt.
You are enough. Just as you are. You are important, influential, and complete.
The world is big and scary, yes, but music, moonlight, birds that dance to music, and little kids who make potions out of dirt and rainwater exist, so it can't all be bad, can it?
~If I said anything harmful, please alert me and I will fix it.~