Okay, first off I'm new to this forum so hello! I'm an FTM who has been where you are.
Look, first and foremost, don't believe everything you read online (in reference to your comment about gender identities not changing past age three). Do you remember ever having an identity crisis, or any crisis for that matter from when you were three? I know I don't. I don't remember anything from when I was three. So if you were to rely on that internet posting, who exactly is assigning that three year old his/her gender identity? I seriously doubt it is the three year old. I myself identified as female for my childhood simply because I didn't know there was any other option. I remember looking back how certain things were different about me as a child but to say I knew something was amiss on the scale it was until I was much older would be a lie. It takes lots of time and thought to evaluate yourself and how you feel and from what I'm gathering I don't think you've given yourself enough time even though it may feel like an eternity.
Secondly, you have to give yourself the opportunity to try and not worry about who "lets you live it down". While many people will not understand or even support you, if you want the self torture and wondering to end, YOU have to reach the point where you put your own needs ahead of what everyone else thinks or will hold over your head. Furthermore, why are you surrounding yourself with people who would hold something of this magnitude over your head to begin with?? Those are the people who will hold you back regardless of what it is that you attempt and then, should you fail, rub it in your face. It isn't always easy to find the separation needed to give yourself the freedom to be yourself, but it is absolutely necessary. Allow yourself to be yourself first and the rest will come to you with time and thought. That's simply the best advice that I can give you.
