Irregular periods?

I got my period 13 weeks after birth. It lasted the normal 5 days and was fairly light & cramp-free aswell. Only problem is this month I didnt get it? It was supposed to come dec30, and I'm still waiting for her arrival. I exclusively breastfeed. Me and my boyfriend did have sex once within those 4 weeks but according to glow I wasnt ovulating. Idk are irregular periods common postpartum? Help!