Hi, I Had Protected Sex About A About A Week

Hi, I had protected sex about a about a week ago and 100% sure there was no condom failure, but I think I have missed my period as it normally arrives late in the month and cuts into the beginning of the next month, I was on flucloxacillin for an infection and also had a hangover 3 days after I had sex. I get the usual feeling g as if im going to get my period, but it isnt happening, im just curious as to why it isn coming. (I can sometimes have irregular periods but havent for a while and I cant remember when I had it last)