Why am I like this? Please help!?

I'm just really, really shy. I don't say anything because I'm afraid I'll say the wrong thing. It's something I always worry about. And then sometimes I just let things slip and I say something and U feel so stupid. I just sit there feeling embarassed. And if I'm in a situation where I have to talk one on one with another person, I over analyze everything I said the whole conversation in my head for hours after. It's got to where I can't even update my status or put pictures on my Facebook because I'm afraid people will think I'm stupid. I don't k ow what to do. I'm a 16 year old girl. Is it normal to feel this way? Should I talk to my mom about it? If so, how? And what should I say? Please help. Thanks!