I know how you feel, Cake. I don't have much trouble speaking to people...though I do sort of avoid contact with strangers because I'm shy and reserved, when I am talking to them, I'm cool and clever about it. I'll be honest...I'm a very accomplished smart ass when I need to be. But generally, I sort of "mimic" whoever I'm talking to. I see how they act and adapt my own behavior to theirs, to try and get along better with them. I find myself doing this automatically, and have been doing it for so long that even when I'm around close friends and can be myself...I find I have no idea what "myself" is like.
Writing, though...I can always express myself on the internet or when I'm typing/writing. I think this is because I don't have the chance to "adapt" to people.
I read somewhere that INTP's have earned the title "Chameleon" for the way their intuition allows them to alter their behavior in a way that suits whoever they're around. This describes me pretty well.