How to get a diagnosis

I'm looking for mental health services for my daughter. I have been looking since she was small; she's 18 now. So far, I have found exactly no one who can provide anything she needs for less than several thousand dollars up front, & then a few hundred a week. We have insurance.

How did y'all get an official diagnosis? Or does she even need one?

It took me about 5 yrs to get someone to diagnose her ADHD & even now she's not getting help for that because I can't find any one in the entire north Houston metro area who will see her. It's insane, having all these doctors here but not one capable of taking her as a patient.

I've gotta be missing something right? I don't understand what I'm doing wrong. How did y'all get your diagnosis?