Ever feel invisible?

I'm sure you have at some point. I think it's something most people struggle with every once in a while, if not more often. I know this much to be true (and it was confirmed, once again tonight)--I don't like being in large groups because I feel invisible. I'm not the loudest, I'm not the funniest, and I don't have the most acquaintances. So, these situations are always just awkward and all of sudden give me low self esteem, when just minutes before I was feeling confident and happy. I found it so weird that I had such a great day today with four true friends, spending hours together, walking around campus, talking, laughing, and listening to music, but the second a got around a group of people who meant nothing to me, I felt unhappy. I cherish my close friends so much. But, then I get around people who are outside of my group of friends, and, all of a sudden, I feel like I'm not enough. The others in the group don't say anything to make me feel this way, and they don't have to. Maybe that's the problem? It's when I get around these groups, that I start to think, "Why don't I have as many friends as so-and-so?" "How is it that there are so many people around, but I'm hardly talking to anyone?" Honestly I usually know the answers to my questions. It takes work to keep us social acquaintances and relationships. I've had friends who spend hours a day on facebook, trying to write on a hundred different people's walls, so they can have a hundred different friends, and have built a hundred different relationships out of thin air. I can't do this. It's absolutely not my personality. It has to be real. And, most times, I'm ok with that. Actually, I like that. I like my close relationships and i like knowing that there is a small group of friends who truly care for me and I them. I'm human though, and some days, the pressures of being a 19-year-old girl get to me. Tonight was one of those times.