I Had Sex For The First Time About A Month

I had sex for the first time about a month ago. Used a condom but not all the way. I'm not even sure if he did went all the way. He pre-ejaculated outside of me not in me outside near me. Right away I moved. I freaked out. It was my first time. I'm 4 days late from getting my period. But sometimes my periods aren't regular. I'm worried. But 2 weeks later after having "sex" I started birth control. Maybe it's birth control, maybe it's my body not being used to it that makes me not have a period? Pregnant or birth control?