Spotting/brown discharge a week after plan b

I took plan b an hour after unprotected sex (he didn’t finish inside of me) and my previous period had ended 4 days before this. A week after taking plan B, I started having this brown spotting/discharge with some clots and it’s lasted almost 4 days now. My next period isn’t due till another week. Is this implantation bleeding???

I also experienced extreme nausea the first day of the spotting and slight cramps as if I was on my period. My breasts are sore and my nipples are sensitive (last time I took plan b, I had sensitive nipples too)

Part of me thinks this could just be side effects from plan b because I’ve taken it once every month for the past three months (this is my third month taking it)

But I didn’t have this kind of bleeding the last two times I’ve taken it.

Someone please help me, I’m terrified of being pregnant because I literally just turned 20 last week and I’m not ready to be a mom 😖😭