Is this normal

Hey ladies so I had just gotten my period last month on the 13th of July. Keep in mind I had my son and for a whole year and nine months I didn’t get my period until the 13th of July. Anyways my app said I was supposed to get it on the 9th of August but didn’t get it🙄 And my app says I’m 9 days late. I also just took a test witch in fact came out negative. Yes I have sex with my husband without using protection and I’m not on any birth control since I’m still breast-feeding. Can this just be normal?