Confused🙈🙈

Cass
My due date is October 6th 2016 but I'm confused on when I could have possibly conceived! Any help or suggestions? 
First day of last period was January 6th and it was 7 days long and I'm on a 28 day cycle. 
I don't understand where I started to ovulate. 
HELP🙈🙈🙈