Confused

Ok so my last period was may 18 n the only day possible for conception is memorial day on June 25 I went for my first dr appointment my due date was February 22 n as of yesterday I thought I was 7 weeks n 1 day, I heard the baby's heart beat with a fetal doppler wen I was 6w 4d but then I was having sharp stabbing consistent pain above my pelvic bone in the center yesterday so went to er they did hcg level and its 18,000 did and ultra sound n says the baby is measuring at 6 weeks n heart beat is 196 n due date is feb 27 now I went n counted from memorial day till yesterday n its 5 w n 2 d so none of its making any sense.. Pls help