Am I pregnant?

So, here's the story. Me and my SO basically had makeup sex after a really bad argument. And he came inside twice. I took plan b about 12 hours after. (I'm a bit overweight so I thought maybe it didn't work) now it's the end of the month and my period is a week late. I took 2 pregnancy tests (both in the morning) and both were negative? Idk what to do.