Irregular cycles?

I’ve just recently turned 19 and ever since I was 16 I used a app to track it. And it never failed me came on the same day it says. But recent cycles have been off by a day to few days. I try not to stress about TTC but I fear that’s what makes my periods irregular these last few cycles.

Also anyone else get really tender breast some cycles and some you don’t feel a thing. This never happened to me I always had sore breast leading up to my period also. But I’ve had maybe 1/2 cycles where I don’t feel anything. I ask because last cycle they hurt this one they don’t. And it’s not the first time I’ve noticed this.