As an Aspie in employment, which is the best union to join?

Are there unions specific to Northern Ireland, Scotland, Wales or England? I live in Northern Ireland.

I have been given menial jobs at work and I think I’m being gas lighted. People ignore me and talk about politics and health issues at work. It’s very unprofessional and I avoid lunch with staff so to avoid feeling awkward and under a microscope.

HR by the way are very distant with me ever since I disclosed my aspergers, or maybe since I described insidious bullying and poor treatment at a previous place of employment. Or maybe since I said I contacted specialisterne as they can work with the employer and employee and could provide a service to me. HR did not like this, I knew as soon as I said it. I don’t really know.

I do know that people are keeping me out of the loop (about what I’m not sure) because there’s so much whispering going on and team members are behaving shiftily. All communications to me are being done via email with my manager cc’d in. I am being brought up on minor mistakes which has not happened before.

So how do I go about joining a union because I can see myself being let go from my job and it being covered up as a ‘performance’  or attitudinal problem.

Thank you