All over the place?!

Rosie
Hi ladies,
Is anyone else finding their app is really off for ovulation and period dates? 
We've been TTC number 2 for the last three months. Each month I've been either 7-10 days late for my period. I'm not pregnant (and starting to sound a little crazy every month when I think I am!) 
If the app is off with period dates, then are the optimal ovulation dates are off too?