What happened to me now?

I'm having a problem with my brother. Ever since he came into my life, everything seems to happen against me. Now, I often quarrel with my parents, even over little things and sometimes for no reasons. I don't know why i am getting impatient with just everything. And because of that, i lost my interest in studies and started behaving very badly that even I can't forgive myself... What should I do? Why am I behaving that way?