4th day no period

I've been taking my BC pills for 8months now and I've always had my period on a Friday which is 4th day into placebo week. But today for the first time I haven't had my period on a Friday just mild cramps. The last time I had sex was 6th March which was before my period week and may have had a missed pill on 8th march due to some minor stomach problems although I don't think it was classed as missed (I did get my period that Friday of the placebo week) just a month later nothing. Any chance of pregnancy? I'm worried :(