IBS disappears when I'm not around my parents

So l've discovered that whenever I'm around my parents I will have prolonged IBS symptoms during and after.

When I first moved to university halls and then later with my ex boyfriend I noticed I had perfectly normal and regular bowel movements with no pain, even if I had a stressful day or argument etc I was fine.

I have a lot of fight or flight trauma associated with my parents, and so whenever they are around, even in my adult life I simply can't use the bathroom as their only mode of communication is screaming or shouting or just genuinely behaving like they have O social skills towards other people in the house. My house was always loud when I was young, like super loud, and looking back, I was constipated often when I was younger, now i understand this may of been due to them just fucking up my nervous system.

Recently I've had to stay with them for a couple months in between house moves and jobs and all of my painful IBS symptoms have come back. Help!