No period....???

Glow says I am on the 3rd day off my period, but I am not. I even entered that my period is late. It was supposed to be here the 10th and never showed. All tests are negative so I am sure I'm not pregnant. I skipped back in March and had a period in April. Until March I had never skipped but maybe 1 time. Why is glow saying it's my 3rd day even though I've said my period hasn't started??