Periods before and after birth

We are trying for our second kiddo. My periods before my daughter were longer I think. I didn’t track as closely but I am fairly certain they were longer. My periods after are every 26 days on the dot. Never fails. When I got pregnant last time with my longer cycle, I tested 3 days early and got a positive. Now here is my question. Since I have a shorter cycle now, could it be possible to not test positive until after my missed period? Any body not get a positive with first response until after or the day of a missed period?