Help me! Here’s the calendar month of when i got pregnant.

I’m 32 weeks. My baby is really big and measuring ahead. He’s been measuring 2 weeks ahead for a while. My original dd was July 18th, but at the beginning of my pregnancy they changed my dd to July 12th. Now i’m set to have my baby in June. When did I actually get pregnant? I got my first positive pregnancy test on October 30th. It wasn’t faint either. I took a clear blue digital the next day and it was positive. Was the “period” I had on October 12th-16th really not my period?