i, in a way, know what your going through with the stress, except about your mum.
Just before my 15th birthday my parents broke up, my mum left, and i rememebr her saying that she was going to wait until i'd finished my GCSE's to leave, but that she couldnt wait anymore. I used to be so close to her, and not at all to my dad, but now i hardly see her cos I still cant get over it, and its only just hit me, cos i used to just not care about it, but over christmas I developed depression and i was just thinking all the time, why wasnt i worth staying for? i had to do 2 A level courseworks and prepare for my january exams at the same time, and although i got myself together, i could still have doen better. But i agree, dont be afraid to say you cant cope. im applying for special consideration about my coursework marks so that i can hopefully push the marks up a little, so I suggest you think about doing the same.
I know the circumstances arent the same, and Im not trying to get sympathy or make my own sob-story, but there are a lot of people around you to help and to understand