Please you should have mentioned age anyways Most periods last 3 to 5 days, but any where from 2 to 7 days is normal. Menstrual cycles may happen around the same date every month or they may be irregular. A menstrual period is considered late if it hasn't started 5 or more days after the day you expected it to start. Anyways delayed menses is not just by sexual activity there are so many reasons behind. Too much stress for your body may cause a late or missed period. Yourperiods should come back when you change your activities or situation. In some cases hormone imbalance is causes missed periods. A rare problem called polycystic ovary syndrome can affect a young woman's menstrual cycle. Bad effects of medicine, like you had, being anemic, hormones imbalance, etc so don't worry this may be normal by itself within few days and if you feel any pms related symptoms or any problems consult me online so that I can help you through classical homeopathic remedies.