Fertility schedule after giving birth

Possible po ba mabuntis agad 5 mos after giving birth CS section, april 2 yung 1st period after giving birth and at the time same april 21 din may nangyari? Pure breastfeeding din kay baby now. Till now kasi wala pa ulit ako period. Easy to detect ba fertility nun? Can't calculate thru calendar method not sure pa po kasi sa cycle period ? Thanks sa sasagot. ?