Plan B

I recently took Plan b after having unprotected sex. I’m on birth control pills, but at the time I was taking an antibiotic that could’ve potentially made my pills less effective, so I took a plan B in case. I have two sugar pills left and. I was supposed to get them on the second or third pill. (This week Tuesday or Wednesday). It’s now Friday and I’ve had no signs of bleeding or spotting. I know plan B has an effect on it, but when will I get it? When should I be concerned?