My mother and I got into a very bad argument

My mom and I are close but when we fight, we fight.

My brother is 14 and my family is starting to have some serious problems with him as far as behavior and finding drugs in his backpack, phone calls home from school, etc. He’s rude and entitled and we don’t get along very well but he’s 14 and I’m 20 so I just brush it off because maybe it’s a phase or something.

Wednesday I was out for the day with my mom and my brother, and all day he had such an attitude. In the afternoon we had to drive to a dealership to pick up my moms car from getting an oil change, and on our way there, my brother randomly starts getting very nasty with my mom and I, and starts saying very mean things to and about me, calling me fat, saying that I’ve gained too much weight while pregnant (currently 39 weeks pregnant), saying rude things about my boyfriend and his family, and then he says that everyone in out family hates me and can’t stand me and that’s when my mom jumped in screaming, telling my brother to shut up. When we get to the dealership I called my boyfriend because I just wanted to go home, and my mom gets out of the car and tells me to get back in and I tell her that my boyfriend was getting me and I guess this upset her and I asked her why she was so quiet and then all of the sudden when my brother starts saying “Everyone hates you, no one can stand you” that’s when you start to speak up? And this infuriated her to the point that she started throwing things at me and in my face from the car, screaming at me, telling me what a worthless piece of shit I am, etc.

A woman near by came up to me and asked if I needed help and if I was safe and needed the police, I told her no because I didn’t want the situation to escalate and that I was okay. When she finally let my mom started screaming over and over again “You finally got your attention for the day, give yourself a pat on the back!” She eventually drove off and then called my boyfriend when he picked me up, trying to tell him her side of the story but then when she heard my voice, she hung up. I texted her Wednesday night telling her how hurt and embarrassed I was and I never got a response.

What should I do? I don’t want this to ruin the relationship I have with my mom but I’m very hurt.