You're kind of mixing apples and oranges.
My kids are very polite. That doesn't mean they don't have mental illnesses.
Only a child/adolescent psychiatrist can diagnose and treat a mental illness. It can take time and astute clinical observation to get there.
My son is a very complicated case. He went through many clinicians until we found a team in Utah who "got" him. Now he's thriving because he feels understood, respected and emotionally safe. That can make all the difference in the world.
I hope you are able to make some headway soon.