*WARNING SUPER LONG* idk what to do or how to apologize to my mom💔

I'm 18 I'm 5 months pregnant, since I was a child loud noises really ticked me off and would start a rage inside of me that I just had to yell to whoever was making it and it just would give me so much anxiety and now that I'm older I know about it more but I just don't know how to deal w it correctly. My little brother has been the best gift god has given to me I've always wanted a baby brother and in the beginning he was my world you never saw me without him. My mom loved how much I loved to help and it was just amazing. I moved out when I was 17 and he was about 2 and me and him just kind of lost that relationship.. now that I'm moved back in he doesn't really run to me or want to play w me as much. And my mom and stepdad have raised him to feel entitled to everything. They don't discipline him and give him everybting he wants he hits them, yells at them, throws stuff at them, and I've kind of been the one to set the standard to 'you respect me' he doesn't do anything but scream at me but he doesn't dare hit me or throw things at me. Earlier my mom and I were talking and hesin between us playing w a box and his toy and he kept moving the toy inside to The point where it was making such a loud noise where my mom and I couldn't hear each other. I calmly asked him "can you stop mami and I are trying to talk" he screamed back "NO" like the usual and kept going. It got extremely loud cause he just KNEW it was bothering us and so I yelled super loud and told him to stop and he got so scared he jumped frightened and started screaming no and kept doing the noise, I'm now thinking about it and I feel super guilty and sad Bec I jsut love him so much and I hate that he kind of hates me, and I know I'm disrespecting my mom by not following how she's raising her own son. When she raised my sister and I she was more on the tougher side with us she's the complete opposite w my little brother. I'm not jealous or anything it just bothers me that I know how strong she is and how she likes to have respect from her kids but let's him do whatever. And I know for a fact I wouldn't like anyone yelling at my child that way I need some help and advice on learning how to deal and cope w my anger... some one please help me. My doctor is fully booked and the next available appointment wouldn't be till 2 weeks from now..