BJ, I'm sort of the mirror of your situation. I've been pondering the same question, only I was born male. I started really exploring all of this about two months ago, and it has been hard. When I first decided to face this, I felt scared, and confused, and sort of like something might be wrong with me. But over time, I've been able to calm a lot of my fears and learn to feel a bit better about myself.
There are two things that helped me out, so I'll share them with you in case they might help as well. First was understanding that being transgender does not necessarily mean being transsexual - i.e. actually transitioning. We as a society like to treat gender as a binary thing, but if you think of it more as a sliding scale between male and female, things become easier to grasp. Just because you're a tomboy doesn't mean you want to be male. Maybe you just don't like the typical female archetype. And that's fine. Maybe you were born female, but you just have a more masculine personality. Also fine. Maybe he just like male clothes and activities more. And that is fine too. Or maybe you were born female and what you need is to transition. All of these are fine, and all of these are 'transgender'. If you think of it more as a scale like this, it makes everything a little less scary to explore. You're not trying to find out if you want to become male - you're just trying to figure out how uncomfortable you are with being female and/or how comfortable you are being male. Not everyone who is transgender necessarily needs or wants to transition, either. So don't feel like you have to. Do what's right for you.
Secondly, if you can, try and find a gender therapist. This honestly has helped me so much. They will give you a safe place to talk about all of these feelings and thoughts and allow you a chance to talk to someone who has some idea what you might be going through. They're not going to tell you what you are, but they'll ask the probing questions that help you figure it out.
Honestly, I still don't know what the heck I am or how I want to identify. It still troubles me sometimes, and I still doubt myself both as a male and a female alot. But I feel alot better about myself because of these two things. So... hopefully they help you too.