Terrified, Am I pregnant.

Êvë • Positive Vibes, Be Happy & Be You

I have never had a on time cycle, and my period is everywhere. But I'm 18 days late (and I was already late when me and my boyfriend had sex) and we did it 3-4 days ago and ever since then, that I can remember (I'm stressed easy) I've felt nausea and like heartburn, but nothing else. I'm terrified, I'm 17 almost 18 and idk what to do. Help?! Please...

Could it be stress, or my cycle? I'm so lost, and scared.