I'm 13 and sometimes my dad can be the best in the world, but he can also be really mean. What do I do?

Ever since my little brother was born he's became more and more distant from me. But sometimes he's really nice and funny, but other times he's just horrible. He'll order me around like he's my boss and not my dad. And being a teenager I'll sometimes scowl or w/e and he'll get really mad. He also says that he doesn't like me I'm a spoiled S**t in front of me and even my mum and my brother. My mum always sticks up for me though. He's also really protective over my brother. My brothers 3 and gets really annoying, like he'll start bashing random keys on my keyboard while im trying to play or steal my makeup and spread it everywhere and I'll have a go at him or tell him to leave me alone and my dad will shout at me even though my brothers the one annoying me. I know my dad has had a history of mental illness and as far as I know he still has Schizophrenia (i don't how it's called xD). I'm just really stuck on what to do, I don't think he realizes how much this hurts me inside and that I now doubt if I'm a good person and it's all my fault that this is happening.