If she's a week late, and you tack on 2 weeks since ovulation, she's around 3 weeks pregnant if pregnant at all. (Have you tested, OP? Hope you are ok over there. Most test are sensitive enough now to catch it 8-10 days past ovulation, and you are past period so ANY brand will do at this point. )
Conception is sperm meeting egg
. Not sperm meeting last uterine lining shed.
Docs ask for your last period so they can guess your ovulation date 2 weeks later from that. They are assuming the woman has the average 4 weeks ish cycle:
2 weeks to ramp up, egg released, 2 weeks egg coming down the pipeline. Egg and uterine lining shed if egg was not fertilized. Start over.
(I do sex ed for kids, I can't help myself.