Did you not have any early pregnancy ultrasounds? Typically they do an early ultrasound before 12 weeks to get an accurate idea of how far along you are. If you had regular menstrual cycles prior to becoming pregnant you can use the first day of your last period to estimate your due date.
okay, but i thought its the scan that tells me my official due date, coz how am i supposed to knw anyway? sorry,am really new to this.
After the first trimester ultrasound dates can be off by as much as 2-3 weeks either way. You should be going by your official due date, NOT the ultrasound dates.