My last period was 16 days ago. If I take a pregnancy test now, will if show up if I am pregnant?

Maybe, but probably not. You should wait until you have a missed or late period before taking a pregnancy test, as taking one too early could cause a false negative if the pregnancy hormones aren't high enough yet to test positive. Typically, once the hormones are high enough to stop your period, they're high enough to be read by most at-home pregnancy tests. Taking one sooner is honestly just a waste of time.