Wrong due date?

Going by my LMP my due date is October 18 going by the ultrsound my due date is Oct 28?? My midwife even said i was measuring ahead with out even using the tape! (14 weeks when i went in.) she told me my uterus was above my belly button and it should be only slightly above my pants not above my belly button yet. And ive been feeling the baby move from about 13 weeks and im 16 weeks now and can SEE the baby moving on the outside.

My son was born 4 weeks early at 6lbs 8oz. Could i be further along and just have small babies so they think im not as far along as i am? I have a gut feeling i should be going by the 18 not the 28 just because of how big i am and such.