What is this?

I had sex last Sunday and he came inside of me. We used a condim but I was still worried. Monday I took the plan b pill. Today I wike up to some blood in my underwear. There wasn't a ton but enough to to need a pad. Now I'm bleeding heavy like I'm on my period but I just had it 2 weeks ago. I'm scared that I am pregnant. Should I be worried or what? I just got off of my period on like the 28th. I'm not supposed to start again until the 24th.