Norethisterone

I have been taking Norethisterone tablets to stop my period while I was on holiday. I stopped taking them as soon as I come back off holiday and I was told that I should start my perios again with 24-35hours. I have taken these tablets before and usually come on very quickly. However when I was on holiday me and this boy got intimate but I cant actually remember what happend. I understand that Norethisterone is not a contraceptive. Is it likely that I am pregnant.? PLEASEE HELP