There was a transgender person on YouTube, several years ago now, who used to say: "If you're trans, you're trans. It never goes away." I'm 74 years old now. And I've been struggling with this as far back into my childhood as I can remember. Of course, way back then, the words transgender, transsexual, & gender dysphoria hadn't even been invented yet that I know of. If they had been, or when they finally were, I never heard of any of them until a dozen or so years ago.

You asked about possible causes for gender dysphoria, other than autism. I can only talk about my own personal situation since I'm not all that well versed in the research that has been done on GD. In my own case, I've waffled back-&-forth between believing I was transgender from birth to concluding my gender dysphoria was simply one aspect of an unrecognized and untreated broader mental illness that also included depression and generalized anxiety. But, of course, the reality is I'll never know. It's sort-of a "chicken-&-egg" kind of question. (I think I could also make a good case for complex PTSD. But the reality is my gender dysphoria related feelings far preceded the cPTSD-related experiences I had.)

Most transgender people I've had contact with (primarily on-line) I think accept the idea that being transgender (and thus experiencing gender dysphoria) is the result of processes that occur in utero. I don't know if I buy that entirely, at least in my case. But I don't know... I suppose it's possible. It seems to be the accepted theory at present. Under any circumstances, it's all academic in my case at this point. My best wishes to you, though, in figuring out your own gender dysphoria.