Argh what am I going to do??!! My mum is actually mad?!?

I think shes bipolar or something like that. Shes always in a mood, drinks way too much and even though me and my sisters dad died in november she doesn't give us any support, just says why aren't you crying? And makes it like a competition of who's cried the most!! Also, for the past two weeks when we've got in from school shes slopped up our dinner and then just gone to bed. And then when she wakes up at around 8 she comes down and starts shouting about my aunt and grandma, calling them 'dirty B**tards' and 's'. If I say anything along the lines of shh i'm trying to do my homework, or don't say 'yeah you're completely right' then she hits my round the head or shouts at me or trys to break the laptop. She is just completely ridiculous and its annoying me so much. Shes always been like this but now shes getting really bad and not a day goes by when she doesn't drink at least 2 or 3 cans of drink, shout at me, have a row with my family sleep or have a fight with me.