plan b taken but unexplained bleeding a week later

I started my period the 6th of this month, had unprotected sex the 12th of this month. my cycle is normally 23 days. I took plan b less than 24 hours after the unprotected sex. it's now a week later and I'm having light bleeding, a pinkish brown color. I'm worried that I'm pregnant and that its implantation bleeding. The bleeding could also be a side effect of plan b, but I thought the side effects only lasted the two days you took the pills.

[John Kim, M.D.]

It could be normal after plan b but I would see your doctor for a blood pregnancy test to make sure.