I hope that by pill you mean Emergency Contraceptive pill. When it is taken, the menses do come within 7-15 days of intake. So wait and see. if the menses have come, it's okay. If the menses don't come for 15 days after taking pill and if you miss the period date, so a urine pregnancy test on an early morning sample in a LAB. This will help you diagnose pregnancy at the earliest. Pills can fail too and hence if you do become pregnant, you must know about it at the earliest so that you can think of other means.