Pregnant or naw?

So 4 days before my last period, the condom came off and my boyfriend came inside me. I took a plan b pill within 12 hours, and then started my period a few days later. Now, I'm 12 days late. I've done 4 pregnancy tests since the day I missed my period, and they've all been negative. So is this stress, because of the plan b, or should I still be paranoid that I'm pregnant?  Gimme your opinions plzzzz