What is my mum's problem?

Im having problems with my mom and dad atm, I have alot of work at school atm and then exams and studying added onto that, I'm really stressed out and sometimes feel really down, my mum and dad pick up on this and instead of trying to be nice they get angry, shout at me, hit me and ground me for being sullen and upset around the house. obviously this isnt helping the situation as I am slightly depressed and have turned to smoking. I try to reason with her and tell her that I have a lot on at the moment, but she's a teacher, has a lot of work too, and so she shrugs it off and undermines it, saying that she has more than me and that I should easily manage. I cant explain to her whats up and being grounded makes it even worse as my friends are the only things that make me happy, any ideas of helpful ways to stay happy or at least deal with my mum until the term ends?