Missed period, 1 positive test, followed by negatives

Hello! This is my first time sharing anything. But I'm confused as hell here! I've had this app for a year and it's amazing. Even just for tracking my periods! I have it down to the exact time of day my period will show up. My husband and and I just started TTC #1. We are in no rush and figure when it happens it happens. I was supposed to get my period last Thursday, a week ago October 1. I am never late by even one day. I didn't take a pregnancy test until Sunday morning and it came up positive. I still have no period and light cramping throughout the day since last Friday. I took another test last night (2 actually) and both negative, took another one first thing his morning and still negative. No sign of AF or my severe cramping that accompanies it. Could this be a chemical pregnancy, just a fluke positive Sunday? Anyone had this expierence? Thanks :)