Conception or implantation?

I keep asking my midwife when I conceived and she keeps coming back to me with ‘it depends when implantation happened’.

I’m due September 12th but I kinda wanna know if I could of conceived from I/course 2nd December or 19th December for personal reasons.

I had a period like bleed after the 2nd December I/course but I had no implantation in this pregnancy..