A little late to this but, depending on your goals for obtaining an official diagnosis, you may not need to get an assessment. When I was diagnosed I had originally started seeing a therapist who referred me to a psychiatrist. The psychiatrist asked me some questions and diagnosed me through an interview and was able to prescribe based on that. I'm sure this varies between states.
Eventually I had to go through diagnostic testing, but only to get testing accommodations for school.
Illegally small borb