period and EBF

So my period may have returned 3/26. It was very dark but lasted a few days. It occurred 28 days after my D&C to remove retained placenta. Here I am 5/2 and nothing. Baby will be 19 weeks on Thursday. Should I be concerned? Can't remember if we had unprotected sex in April or not. How likely is it that my period is just not regular from breast feeding and being postpartum?