Being articulate (or not).

My inability to be articulate has really been getting me down lately. I struggle so much with putting my thoughts into words. I want to be able to talk about my opinions on certain issues; I want to share what's on my mind with others who are as interested in discussing similar subjects because, as my social psych professor said, sometimes talking about things in groups can help you understand or become clearer on certain points, or even generate new ideas. But if I can't even figure out the right words to put forth the thoughts I have, how am I supposed to get anywhere? It's just frustrating, and I'm not sure what to do about it.