4 tracking apps

la

i have for period tracking apps (pathetic i know lol) ovia says i should start the 19th of November which would be a normal 28 day cycle for me (but my period was irregular last month so not sure) flow says i should start the 21st. glow says i should start the 22nd and fertility friend says the 25th. im so confused. and i got all apps at the same time