I'm very lost in what I want to do in life. I'm also lost at who I want to be. Or who I already am. Is this personality I have really me? Maybe this isn't the only personality i'm capable of, maybe if I really got out there I would expand as a person. Maybe there is more to me than what I can see right now.
There are a lot of folks that don't know what they want to do in life. I'm one of them, just to put that out there. I don't know anything off the top of my head that I could really enjoy and find fulfilling. I'm currently working a dead-end job that's absolutely mind-numbing. I can definitely tell you where I don't want to be. If you have the opportunity, try a few jobs in different fields. Maybe you'll find some inspiration.
As for who you want to be, that's completely on you. Your moral compass will help guide you, if you listen to it. The best thing about being a human is that nothing is set in stone. If you wake up one day and decide "I don't like being a doormat", you can formulate a plan and execute it. You can completely change how you interact with the world.
Lastly, I really do think that, unless you have some kind of mental illness, that your personality really is you. There may be aspects of it that you do or don't enjoy, and that's fine. There are certainly ways of influencing and changing your personality. That'll happen over the course of your life. Experiencing more of the world and the people living on it will, most likely, have an effect on you and your personality.
I think that if you were ever to completely quantify your entire personality, you'd probably be a robot. Self-discovery is an exciting and unsure adventure!
You may be suffering from one of society's biggest myths. The truth is, nobody with even a shred of truthful introspection under their belt can definitively conceive of who you are. Their is no definition or summation of you because you are dynamic collection of perspectives and perceptions. Never bring yourself down because you somehow fail to know yourself. Instead, approach introspection like a gleeful and inquisitive scientist, picking apart your own reasoning behind your actions. The best part of this process is the license it gives you to go out and experience the world in which you live. In other words, quit worrying and go out and experience something. You will come to know yourself through those experiences.
I'd just like to add that I'm the same way. What's helped me a little is to just not stress out over it too much. I assume you are fairly young still and that leaves you with a lot of time to figure these things out. I was loosing my mind trying to decide what my career path and future was going to be that I didn't realize that you don't have to find one job or career and run with it for the rest of your life. Try something. If you hate it, move on. If it's not half bad stick with it or look for something similar. You'll find something eventually. Best of luck.