(This was born of a discussion in the transgender community, but I'm making it a post here because I think it will go on long and I think my thoughts are wandering far enough that it may not be directly relevant to the fears or concerns of the OP)
I don't believe it when any trans person says they've never questioned that they were male/female.
I can certainly understand why so many people say it, because we live in a world where trans people's genders are either disallowed or tolerated only with clear evidence (usually something meaningless like passability or one's genital configuration). If the answer you're supposed
to give is the opposite of the one you're giving, then admitting that there's ever been any doubt offers a clear opening to religious fundamentalists, radical feminists, anti-LGBT hate groups, hesitant friends, resistant parents, frightened lovers. Admitting any uncertainty can come off as an admission of guilt, because we are guilty until proven innocent, and in many people's eyes we will never, ever be proven innocent.
What's more, one never hears cissexual people -- whose genders have the clear-cut undeniability that most trans people long for -- admitting to having doubted their own genders. And I have no doubt that the overwhelming majority of them haven't, but I also don't believe that it's because their genders are firm and real. Cissexual people never doubt their genders because cissexual people live in a world in which there is no room
to doubt their genders.
See, there's this idea that seems prevalent that doubt arises from being wrong, when in fact, doubt is simply the natural effect of having multiple realistic options. Cissexual people never doubt because they are not offered multiple options -- a cissexual man who likes being a man will not only never be given reason to consider whether he might really be female, but is bombarded with cultural messages that tell him that doing so would be sick, silly, wrong. His lack of doubt isn't because he's definitely a man -- although he is -- it's because he is only presented with one option, and since it's a satisfying option, he'll never need to look further.
It's worth noting that most of the cissexual people I know who have expressed or implied any uncertainty about their genders have done so as a result of coming into the orbit of the transgender community (usually as a result of a partner or friend transitioning), because in the trans community, an endless banquet of options are on the table: in the best parts of our community, one is free to be male, female, both, neither or something else entirely.
But even before or without becoming involved with the trans community, multiple options are on the table for trans people -- and what is more, we live in a world where choosing the best one for you can subject you not just to scorn and derision, but a seemingly-insurmountable wall of very real difficulties and dangers. With even the tiniest bit of reflection, who could possibly look that in the eye and not
wonder if maybe they'd be better off going the other way? Who could be told from every corner they're wrong and not wonder even once if it's true?
So, yes, I will confess: not only have I doubted in the past, I still doubt sometimes. I sit up at night sometimes and look at all the change in my life and I wonder, What if I've been wrong? What if this is a mistake and I should have stayed a furniture mover?
I question myself all the time -- how I know I'm right is that the answers never change.