Plan B Bleeding

So I'm not asking for hate, I practice safe sex and I'm not inexperienced I just don't use emergency contraceptive a lot so I just have a question. I had sex right after my period ended and we had a mishap where the condom slipped off. We're pretty sure that nothing came out but got plan b just to be safe. I took it within like 2 hours of having sex. Maybe 5 days later I started getting brown discharge then a full on period that required tampons and lasted a normal period length. After that finished, I noticed that my cervical mucus indicated that I was ovulating. So my question is did the plan B force me to shed my uterine lining so the egg couldn't stick even if it was fertilized? Or did I go through a full cycle in like 5 days?