Hi and thanks for the query, It would be very difficult and not very physiologically correct to relate the sexual intercourse of friday to your lack of periods the next day. However, excitement could lead to certain physiologic changes that affect onset of menstruation. It is also important to note the regularity of your cycle, and whether you had not had previous risky sexual exposures before this one. If its the case, you might need to visit your primary care physician for a pregnancy test. If not, you might just need to be patient for the cycle to come. thanks and best regards, Luchuo, MD.