Am I pregnant?

I just got off of my period 4 days ago, went to the bathroom and saw there was a spot of blood on the tissue. I have been on the birth control pill for about 6 months now, I take it everyday, around the same time. My boyfriend accidentally came inside of me the other night and I took a plan b within 24 hours, so I’m wondering if Plan B’s make you bleed sometimes? I’m really confused. And can Xanax and Antihistamines lessen the effectiveness of birth control or the plan b? I took a half of Xanax about 10 hours after taking the plan b and an antihistamine the night after.