I have this feeling all the time, even though I've taken thousands of tests that specifically say that I am most likely autistic. I suppress the thoughts telling me I'm not, and avoid things that might turn the idea into a different thing (if that makes any sense).

Imposter Syndrome. Really a b!tch. My best advice is just, if you're worried you're faking, you aren't. Faking is intentional. If it's happening when you're alone, it's not for attention. You are experiencing these symptoms. Only you know what you experience and self diagnosis is 100% valid <3