periods

I received my first period last month after giving birth. I am currently breastfeeding. Normally my cycles are 28 days. If that’s still the case I am 3 days late. pregnancy test was negative two days ago. When I was pregnant with my now 9m I took a test a day before my period was supposed to come and it was positive. So is it just the breastfeeding that’s making my period late? Is anyone else having an irregular period now after giving birth?