I'm sorry that you are under so much stress. Are you doing actual work or are you just studying in order to get ahead? If you are spending 5-10 hours per day completing assignments, I would talk to your teacher. I'm sure they would appreciate knowing if their class was having to spend that much time (obviously, it was too large of an assignment or the students don't know the material well enough due to lack of teaching).

Do you have a school counselor at your school that you could go talk to? It sounds like this is not something that you can keep at for the rest of the school year. It's vital that you figure out how to regain some balance in your life, because you're right - you can't do this. A school counselor might be able to help you figure out study strategies that could reduce the amount of time you spend on homework, help you with time management, and/or at the very least, assist you in figuring out how to approach your teachers and/or parents about this.