Do you have someone at school to talk to like a guidance counsellor. They are in a position to get things rolling - with or without your parent's permission. Similarly, you are old enough now to make your own medical decisions. Your family can't stop you from going to your family doctor and asking for a referral to a psychiatrist (my recommendation) or a psychologist. Find out the number to the kid's help line in your state/country. Find out a crisis line number locally.

Finally, suicidal thoughts and ideation are serious. Do you feel able to or have access to get to an emergency room? If not the crisis line should be able to help you with that.

In the meantime, I want to say your story really touched a nerve with me about my own mother and my lack of self worth. I only wish I had addressed the situation then instead of waiting until I was 48. You are worth being a friend and it is okay to make mistakes and not be perfect. One of the things I wish I had done - in addition to reaching out for help at school - was to talk to my mother and ask her why was it important to her that my marks be perfect?