Okay I need help

I had sex a little over a week ago for the first time, It was the day after my period ended and we didn't have a condom and had no intention of sex and he pulled out but I'm smart enough to know that you can still get pregnant from Precum. I took plan b around 2 days later and now it feels like I am on my period but the bleeding is a little different. Please tell me What is going on.