California still sounds lovely

Life is so overwhelming.

Every time I try to stay positive, be a good person, there is something that brings me down, gets my thoughts out of wack, and of course, gets me to react in a negative manner.
I don't want to. I want to be good. I want to be loving. I want to be God's servant. I just have the hardest time doing so. Especially at home.
Mostly at home.
There is so much bugging me about the way I live.
For God one minute, for myself the next.
Being all happy and giddy and such one minute, then the second my sister does something to offend or irritate me, I go into personally punched mode and get either defensive or I breakdown.
When I get defensive it's not a good thing. I usually fight back verbally or physically. Punching and screaming and such.. it doesn't help. It just makes it all worse.
I am trying to ignore it when they try to start something, but it's eating away at me.
I have no idea what to do.
God help me.
God, I am trying to live for you.
Please help me.