Pill and period

I'm on the mini pill and have an 8 1/2 month old. My periods have been a little all over the place from when I started it. I've been on it for about 5-6 months. The gaps between periods have gotten longer. But this month I Havnt got my period yet. 7 days over what my last period month was. I had a 20 day gap. So this app gave me a little more time and now I'm 4 days over that. With no sign of a period. I'm breastfeeding my baby regulary. My main question is: has only on the mini pill and breastfeeding had there periods stop again?  I've taken a pregnancy test and its come up negative. So I'm not sure what the go is. Any help would be appreciated !