Plan b....A little help here

Technically I'm in my fertile window rn. But I took plan B last week when I had unprotected sex. I've taken it before but this didn't happen. Is this normal??

UPDATE: I had unprotected sex Friday night (11/24) / Saturday morning. However I couldn't take the pill until that Sunday night. I'm just wonder if everything is alright here, because I've taken it before and my periods came on time as usual.