Need help!!

Okay so I looked at my period app this past Thursday to see when my next period was and it said Friday was going to be my starting day. Well then I looked at my period app again Friday bc I noticed my period still hadn’t started. Well it keeps on changing like I was supposed to start my period Friday and here it is Sunday and I haven’t started. I looked at it today and I’m supposed to start tomorrow but every tine I look at it again it gives me a different date. So like can anyone tell me what’s wrong? 😂🤦🏼‍♀️