Is this normal ??

Sara
When I was 7 weeks pregnant I did an altrasound to hear the baby's heart beats , my EDC was 22/9/2016 . Few weeks after my EDC became 24/9/2016 and later on changed to 26/9 . NOW I suppose to be 18 weeks tomorrow and my EDC is 30/9/2016. IS it normal to have this differences between EDC s ???