I beg to differ, Yasmin, you aren´t shy, you are insecure.
This happens with subjects we think we don´t know enough, or when we have to talk to people we don´t know or we know they are in the same level but in front of a superior, a boss, a teacher, etc.
You may be the shiest person in earth, but if somebody ask your the time (in Portuguese, you will say "são tal e tal hora e tantos minutos'', why is that? because you feel you master that in Portuguese, knowledge is power.
Another example would be, if somebody (even tough he/her is your boss) says that 2 plus 2 is five, you have a knee-jerk (instinctive) reaction, "it´s four" or "no, two plus two equals four.'', see? all of sudden you aren´t shy anymore.
But don´t worry, don´t sweat it, you are in good company, there is a lot of people that are shy (including me).
Anyway, I try my best to broke this natural barrier, by expressing myself and not worrying much about making mistakes (I sweated by the mere tought of having to speak in front of an audience).
Sometimes I even stutter, but I go ahead anyway (just that I slow the speaking when I feel I am anxious). I mean, in Portuguese, my English is not that good, as you might have noticed, so I didn´t made great forays into the language, anyway the times I had to interact with foreigners they understood me (don´t know why!)
Believe me, the very fact of letting people know that you are not a superwoman (or superman to many) gives you an advantage. Everyone likes humble people, but people that interact.
With time you will be talking, writting, wathever you have; and nobody will be even noticing.
I read that you came this Forum and you just read, and didn´t even wrote something, then you, by degrees began to write. See? that´s simple like this!
Ah, the talking about cook will place me in deep waters, my wife complaints about my skills at the kitchen. By the way, I cried like a baby there (peeling onions...), till the day she taught me to bite a match stick, believe me, it works!