Has anyone tested positive weeks after a missed period?

Samantha
The first day of my last period was March 15th. My period was due again mid April. I took a First Response test the day I missed my period & it was negative. I tested again 4 days later. Negative again. 
I haven't tested since but don't see a point? First response is 99% accurate the day of a missed period. 
My friend has me second guessing everything. She said maybe I ovulated late and we conceived right before my missed period? Is this possible? To conceive the day you miss your period but not have enough of the hormone to test positive? 
I am on day 56 of my cycle & wondering if maybe my friend is right?