AITAH for thinking it's my dad's fault if my special needs brother is injured?

I (21f) was staying with my dad for some time, he charged me $500 a month for rent despite me making minimum wage, and being disabled (I got autism and adhd). I was responsible for feeding and bathing my brother (9m) who has Down Syndrome. Problem is, my brother likes to smear poop all over the walls. He has gotten poop on me before and that sends me into rage. I have Bipolar 1 and BPD, at the time, I was off Bipolar meds for two years mistakenly. I have hit my brother whenever he pinches me in the shower and I allowed him to slip and fall out the shower. My dad says I shouldn't hit him and I told him that my brother is disgusting. I have yelled at my brother. My dad never bathes my brother, my mom (parents are divorced) does it. My parents know I am at risk of being violent.

I have had meltdowns over having to clean my brother's poop. AITAH for thinking that my father is/was responsible if I injure my brother due to Bipolar 1/BPD rage?