Are you seeing trauma specialists? I feel like maybe that factor could be a game changer.
My T history is sort of weird. I appeared to have depression and GAD when I was about twelve. My parents were positive I had been sexually abused and erroneously assumed it had been in the previous year or otherwise pretty recently. They stuck me in therapy with a T who specialized in children and sexual abuse, where I was diagnosed with GAD, and then a couple of years later I disclosed my much, much earlier CSA by my brother, who was then compelled to go to a T himself, and I really don't know exactly how all this shit worked out legally, but basically his T was able to inform my T of my brother's sessions, and I was even able to meet with my brother's T and get information from him about the black holes in my memory, which reeeally solidified my diagnosis of PTSD, I'd say, for my T.
My current T--who specializes specifically in PTSD--didn't diagnose me with PTSD until I was able to actually tell her about some of the trauma, which I did via email in a fit of rage in response to knowing she did not have my diagnosis down as PTSD (which felt frustrating and invalidating).
Anyway, all this to say, when I was very young, it was pretty clear that there was something deeply the matter with me, but all through this mess, I have maintained a consistently flat affect, and I've been exceedingly high functioning. However, it's my impression that those who specialize in trauma and PTSD are better equipped to read someone who isn't overtly presenting as symptomatic, and they seem to be better at understanding stoicism as something that is just as often present with PTSD as is hysteria (forgive the anachronistic double-entendre)?