Hi, It would have helped to know what birth control you are actually using as they all have specific timing for starting as well as the day when they actually become effective. Neverthless, I understand that you may be using some hormonal preparation, either pills or patch or something similar. Most of the hormonal methods need to be started on day 2-3 of the periods and continued for 21 days or 28 days to be effective from the day of starting. Since you had started to bleed after you took medicines, the chances that you had any eggs capable to be fertilized at that time are very low. If you began the birth control on day 2-3, again these chances are low. So, your symptoms may be due to indigestion or due to the pills that cause nausea and fatigue. If you are in doubt, you can do a urine pregnancy test 3 weeks after the act of sexual episode to rule out pregnancy. So please do not worry as you are most likely not pregnant. Thanks for the query and it was a pleasure answering your question. Have a good day. Dr. Madhuri Bagde Consultant Obstetrician and Gynecologist