Why is it that i know my 8 year old is autistic but so called doctors and teachers don't think so but they haven't even done any test?

Hard to say: Autism is usually evident by age 2, while other forms of the spectrum can emerge later. Not all unusual behavior is within the label, and docs & teachers have a vested interesting in finding and treating cases. You can have your child evaluated privately through an educational psychologist & developmental pediatrician. Perhaps they can confirm your idea or fine a better label.