There are various reasons for this like ovum not being formed, polycystic ovary, hormone imbalance, hypothyroidism, local infection, blocked tubes etc. In
males it can be infection, STD, varicose veins
, hydroceles, poor sperm count, not enough motile sperms etc. Since a confirmed diagnosis cannot be given on net and without running some basic tests please discuss these possibilities with your gynecologist once.