Hi there..If you got your periods one week after the sexual contact, then it is very unlikely that you will get
pregnant. However there are rare cases where such things can happen. Also are you noticing any signs of nausea vomiting increase size of abdomen? Whatever may be you need go and consult a gynecologist for the absent menstrual cycles. Because sometime even pcod fibromas or any drug intake also can alter the menstrual cycles. The gynecologist will evaluate you for all these things