Condoms birth control sex

Hi, so I'm 20 years old and not that experience about sex. But when I do have sex all I think about afterwards is "am I pregnant?" I am on the IUD. I got it in November. They guy I had sex with I made him use a condom. And my periods don't happened every month. But I had sex Friday and I started my period today (Tuesday) does that mean I'm not pregnant. Or would I still have my period since it was so close to when I was due to get it? Sorry this all may sound dumb. Getting pregnant isn't the worse outcome but I'm just not ready for a kid right now! My brother and girlfriend are actually having their kid today!