Period is back on my ovulation week

I cannot find exactly where to put this question. I’ve been tracking my period on here for 4 months and have never had this issue before the app tracking or after. This week is supposed to be my ovulation week but my period is back instead and I do not know why. I had a miscarriage in December 2018 but it’s been regular before and after that so does anyone know why this is occurring? Now the chart moved my ovulation week to next week. I’m so fucking confused and frustrated.