Late period

Amanda

I’m almost 5 months PP and had my first period since giving birth last month. Now according to this app I’m currently 4 days late. I took a pregnancy test and it was negative just to be sure but is it normal for your periods to be irregular after birth? I’m exclusively breastfeeding too so I was thinking maybe that could be why, but I’m slightly freaking out lol before having my son I was always regular and on time every month.