I don't know the person I'm becoming.
That's a bit vague, is there something specific that is going on with you?
I'm becoming someone that I can't even recognize myself.
Everyone has doubts about them themselves from time to time, but it's important to try to stay true to who you want to be. If you find yourself changing into someone you don't want to be, you should make an active effort to stop those changes.
I don't know if I'm capable of doing that.
As long as you are not lying to yourself or being fake with other people, I think you are doing okay. Try to focus on the person you want to become and worry less about the past. I think you'll overcome this existential crisis.