As has been stated, MANY trans people know from very early ages that there is something different about them that is related to gender. Similar to gay people, they knew that what they felt was counter to the expectations of family, friends, teachers, etc.
Transitioning, or not, is a very difficult thing to sort out by yourself. I suspect that because transitioning effects so many facets of ones life and can bring about MAJOR changes in ones life, conscious thought about it is hard to do. Our minds want to avoid stressful activities and so we don’t think about what we need to think about.
This is why many members have found positive benefits from working with a therapist. However, it shouldn’t be just any therapist. It needs to be someone with experience in gender issues. Not every therapist has this background.
Now, it does turn out that some crossdressers do turn out to actually be transgender. Anecdotally, it doesn’t seem to be a large percentage. It is difficult for researchers to get funding for studying transgender issues, so many questions remain unanswered or partially so.
Anyway, there is no rush to sort this all out. Haste is not your friend here. If, in fact, major changes to your life are warranted, you need to be really comfortable with what will happen. The middle of transition is not the time to be figuring stuff out. For the most part, that should have happened before.