due date?

so i have been to 3 ultrasounds. the first being when i was 7w5d, confirming my due date of November 3rd. My second one being 2 weeks ago when i was 12weeks exactly. which the baby still showed to be on track with my due date. Then i just had one today & now the baby is showing to be 16 weeks when i thought i was 14w 3d which would bring my due date to October 23rd.. has this happened to anyone else?? i just find it weird i just had one 2 weeks ago & the baby was matching the november due date & now all of a sudden it's 2 weeks ahead??