When to get a pap smear

[cattylina.livejournal.com]

I'm 18 years old, and I've recently become sexually active (in the past 4 or so months). Thus far, I've had sex with two women and one man. I didn't use protection with the women (I know, I know...), and I was very, very careful while with the guy; he wore a condom and pulled out. I also take Yaz. My question is: do I need a pap smear? I've heard that you should start at 21, but my mom stressed that as soon as I became sexually active, I needed one. It'll be relatively easy; my campus health center has a great gynecology department...but I'd rather not have one unless it's absolutely necessary.