Late period while breastfeeding?

I got my first period when I was 6 months pp. I’m usually a regular 28 days. Last month, I was two days late, now this month I’m 5 days late. I’ve been cramping these past three days, no sign of bleeding. Felt a little nauseous & light headed. Maybe because I been doing a lot of house work. Only happened once, took a test & showed up negative. We barely have sex but when we do, we use condom. Idk what’s going on, is it normal to be irregular while breastfeeding? This is making me nervous ...