You are a sweetheart.... a true Angel....
However long you may live, you will never get your childhood back... So, ENJOY.... and you read it right... enjoy all your bits.
From your language, it's evident you are an outstanding student. MARKS ARE NO PARAMETERS TO PROVE THAT.
Formative Evaluations (what you call, unit tests), are simply intended for the teacher to 'evaluate' your learning, NOT YOU. It is intended to test the extent to which you have comprehended what the teacher has taught, AND THAT'S IT. Don't cram up stuff you don't follow; take help and understand.
1. Define your Home - Work. Decide what is URGENT and what can be postponed.
2. Do only that urgent job (Be it limited, but do it well)
3. On the days when you have an off, add 4 to 5 hours of sincere applications and do the rest of the work; but do that too, very well. It is futile to copy stuff from the 'guide' inorder to 'complete' your book.
4. When you get too big a home work, stand up and tell the teacher that she reduce the work in lieu of the assignment from other teachers.
5. Revise your work daily. REVISE not REREAD. In the sense, every night, before going to bed VISUALISE what happened in the class from the first period to the last period. It should take no more than ten minutes.Get your mummy to volunteer. She will hold the time-table and you would rattle out all that you did during the day. THIS IS A VERY POWERFUL TECHNIQUE. Not only does it develop the memory; but also encourage you to pay attention to every facet of your teacher's instructions. You'd go a long long way. God Bless You