Hi Gwynivere,
As everyone says, see a gender therapist. But I can tell you that not every transgender person knows from a young age.
I say this because I didn't know until my early 20's, and wasn't certain until quite a bit later.
Sure, I can look back to younger years and say "Oh, that makes sense, now!"
But I simply did not have a framework to understand myself when I was younger. That, or maybe I was really good at repressing things. Actually I know I was good at repressing things, but that's another story.
My main point is don't let anyone tell you who you are or aren't just because you don't fit a typical pattern.
Everyone is different, (and I mean everyone, not just the trans community) and while there may be common themes and experiences. Those are just the "averages", your experience doesn't have to fit in a box of what's usual.
Sorry for the mini-rant, but I feel quite passionate about this.
Btw, welcome to the forums and good luck on your journey.
~Dee.