To estimate a conception day you need two pieces of information: the date of your last menstruation and the normal duration of your menstrual cycle. You've stated that your cycle duration is (120 ) days. Women with such a cycle duration usually can’t get pregnant. If you really started your last period on the 17th of November it is impossible to have conceived on November 19th...December 9th is a more likely and possible conception date, but even then the menstrual cycle should last more than 34 days which is also less possible. Are you sure that you didn’t have sex at the end of November or at the beginning of December 2007?