How can I control my anger?

It's only really my boyfriend and my family I get angry at. It's over the smallest things though and I just snap. I start by getting frustrated and walking away and then throwing around excuses and critizising the person when I don't even know why i'm arguing in the first place. I try to take deep breaths or do something that distracts me but no matter what, my anger builds up and up and I make the argument worse by throwing in anything completely irrelivant that's ticking me off and blaming them. Then I get upset when I realise I don't even know what i'm arguing about and feel pretty crap. How can I stop it from happening i'm ruining my relationship and becoming really depressed over it.