No second period postpartum

Kauthar

I gave birth the 31st July. I got my period the following month which lasted for 7 days.. Im suppose to get my period this month but it never pitched. My app says I’m 4 days late. I’m exclusively breastfeeding and I’m not on any birth control. My husband and I did the deed a few times with the pulling out method.

Should I be worried or is it normal for periods to skip the second month etc…