I always have my period on the 19th of the month. In March my period came on the 15th. I found out I was pregnant at 4 weeks and the Dr. gave me a due date of Dec. 20th (which I know is not always exact). What I am concerned about was that I had sexual intercourse with someone other than my boyfriend on March 15, 16, and 17th. I got back with my boyfriend on the 18th and had intercourse with him everyday since then. Can you tell me what my conception date is?