I tend to be invisible, too. It used to depress me, but then I realized that it generally only happens in drunken environments (bars, parties, etc..). I think that I simply lack that "party girl" look. Also, in those kinds of environments, I think people have to be extra-outgoing to meet people. You have to be smiling and looking people directly in the eye to be noticed, and you have to be willing to step right up to people and start talking first (don't wait for them to do it).
Relax... I'll need some information first. Just the basic facts - can you show me where it hurts?