Unusual discharge

Hi everyone. I hope someone can help me. I had sex a few days ago and had to take a plan b. I’m supposed to get my period is 4 days. I took the plan b because I had stopped ovulating only a few days before the day I had sex so I thought maybe the app could be wrong and I was at a higher chance for pregnancy. So anyway, now it’s been 3 days since I took the plan b and usually plan b doesn’t cause me any side effects except depression, it doesn’t bring my period sooner, if anything it delays it. However, today whenever I wiped, I noticed brown discharge. It’s only been 4 days since I had sex, so it can’t be implantation. Is this a normal thing with plan b? Could it be that it’s causing my period to come sooner? I don’t see it as a side effect/symptom on the website i’m on.