Confused? Help please

Marian • 22 and expecting a little princess💕🎀
Ladies if anyone can help me I'm a little confused. I saw that group of " when did you concieve" and it just doesn't make sense how some ladies concieved before me or the same date or later on but are due weeks before?.. My due date was changed from the 28th to the 18th due to her being bigger and I thought I concieved my little princess November 7th . Any thoughts?