Me And My Cousin Got Pregnant Around The Same Time

me and my cousin got pregnant around the same time I think & she says that she is 21 weeks pregnant and her due date is March 20th 2016 . does that even add up ? I'm so confused . I've never been pregnant I don't know what to expect .. nothing . but someone else told me that I was only 14 weeks bc I said I was 4 months . I'm so confused . is there anyway you could send me week by week & month by month so I could keep track ?