Do you know if, despite being rare, I might have something else and be mistaken about being transgender

Nope. There really isn't anything that presents as gender dysphria. I mean there are a few things but they're the kind of things that are reallllly obvious just from listening to someone talk. Your psychs would have ABSOLUTELY picked up on that first.

My family did the same thing to me. They weren't anti-trans per se, more like they just didn't want me to fuck my life up by transitioning.

Basically what I told them was like: "Guys, HRT does not cause lasting changes until 5-6 months [mostly true]. And people who start taking HRT who aren't trans get bad mental health problems [Probably true but not really confirmed]. So like look, I've seen 3 psychs - lets just see what happens when I start HRT - I'll keep an open mind to what you're saying but I think that this will be a really good test to see if I'm actually trans"

Also for the record 6 months of therapy is moreeeeee than enough