Why do people in my high school treat me as if I’m autistic ?

I’ll preface by saying , I have nothing against autistic people . I think differences should be celebrated and I’ve met some who are genuinely amazing people . But I really hate how I’m treated by most of my family and peers at school it seems . I’ve been spoken to by multiple professionals who’ve said I don’t have it , done thousands of online quizzes and I have next to no symptoms of it . I feel like Im constantly being patronised or spoken down to which is why I prefer to avoid social situations . I’m definitely an introvert and I do have pretty bad anxiety but I don’t understand how that leads people to assume I’m autistic . I’m extremely quiet and do have some communication issues due to my anxiety , so I prefer not to speak but whenever I do my thoughts always get downplayed by my friends . They’ll also fully explain something that they would just say to someone else normally in passing , I’ll admit I have presented myself as being a bit dopey and stupid in the past but I don’t see why that gives anyone an excuse to patronise me or treat me as if I’m autistic or ‘ special ‘ . I’m also called degrading terms like ‘ spaz ‘ by my friends from time to time which leads to me constantly questioning what their intent behind it was . Even if they’re not trying to treat me as if I’m autistic , people definitely treat as if I’m stupid or inferior to them . I have no idea what to do but I know I can’t live like this much longer . In my last year of high school btw .