I second to keep testing atleast once a week till it comes back cause like the above comment said if you already ovulated it won’t work. If you can keep stress to a min that can delay your period.
Hey, this happened to me this month. My Flo got heavier as the days went by. Because my Flo app said I was like 3 days late but I was just spotting, especially only in the morning after waking. Maybe wait for 5 more days If you tracking your period and then if you still spotting take it again. I am also under a lot of stress and also I have put on a bit of weight .
You could be late because of stress. keep in mind plan b may not work if you are over 150lb or already ovulating. I would test again in about a week.