Giraffe wins with the simpliest solution. 
Or, what my Favorite Aunt ( mother of six) does to get a word in edgewise when the conversation is rolling and she needs their attention is the international sports signal for Time Out. Usually followed by “Hold your horses…what is * this* ?”
Gypsy GirlBTW, I reallllly like your user name , it is ok to clam up in a group setting. You are labeling yourself wrongly. Think of yourself as an observer. And when you do say something, very little is better, everyone will think you smarter than the blowhard knowitall who is on a fillibuster to end all fillibusters. It is all about timing. Everything in life boils down to timing and fresh breath.
I use to get headaches from the pressure of being at parties and social events. I was quite the shy girl in social settings. Cute girl, long hair, big blue eyes, rigid in the group fearful to say anything. ( around family and friends, fergetaboutit.) But I knew I had something to contribute but couldn’t get it from my brain to my mouth without some horrific gaff. The stress of it all. Yes, the same loquacious, effervesent Shirley, stressed out at parties. It’s hard to imagine.
I’d forgotten about my reticence to attend parties until I was cleaning out a bunch of old purses to give to charity and in the little zippered compartment in every one of them was at least a half a dozen tylenol. It was like *oh, yeah, for those headaches that use to come on in social situations…why did I allow it to get to me? * Answer? I was young and insecure, and gradually, like drops of water filling up a glass, I grew into this person I am now, groups setting didn’t bother me. Now, to complete the metaphor appropriately, I am full of it. 
But, not all flowers bloom at the same time.
Take your time, be patient and if all else fails, turn up the stereo and just shout at everyone.