I'm a young adult, and I'm quite obsessed with them. Simply, because they're cool and they add more style to you, and if you're one of those Rock/Metal girls, who love that kind of genre, then they will totally match your personality. You also feel different from everyone else with them on; which is a good thing. Whatever you do though, do not let anyone convince you to stop wearing them or to not get them. Many people don't think they look good; which is their own opinion, but they shouldn't judge, just by what people wear.
I don't exactly know because I don't know your life..but if someone in your family has any piercings..mabye you thought of having piercings too then? It could be based on the type of music you like or your religion or culture or even based on a television show or movie you like? Mabye your favorite famous person has piercings..or idol that doesn't even have to be famous had piercings and you wanted sone? Mabye if your in a certain mood or something. Just some guesses.
I'm having the same problem, maybe it's just because of how many there are and you only have a couple. By thinking having more will show people you don't just have tiny ones that don't mean a lot. That's what I believe but I want more too.