Approaching Diagnosis and Finding a Therapist for Dissociative Identity Disorder

I had a traumatic incident around two years ago that triggered a chain of events that caused me to have repeated meltdowns and brought out alters. I haven't been diagnosed but I have lots of childhood trauma and repeated trauma and abuse up until I was 18 and beyond. having spoken in lengths with my brothers and old friends, and trying to remember details of my own life/childhood, a lot which is fragmented and difficult, there were signs as a child that I had alters(my brother telling me once that I introduced myself as "Fred" and that Fred came out regularly as well as a few unnamed few), for some reasons after a time (I don't know when, maybe in elementary school?) they "hid" and started masking to try to get by, but leaving me going through life confused about who I am, unable to remember things, feeling like an imposter, disconnected from everything and always trying to escape, amongst other odd and specific dissociative behaviors that I recently discovered. How can I approach diagnosis, how can I find a therapist who will be able to look for the signs, or believe me? how can I move forward to getting proper mental health without a therapist that thinking I'm simply self-diagnosing? my last therapist just said I had "garden variety" anxiety and depression, but I always feel like there's something deeper going on. I can't connect with the system but I know they are there, it makes life very conflicting. what should I do?