Hi, and thanks for your query on eHealth forum!
Well, any late period in a sexually active woman should be tested for pregnancy. However, if this time too the test is negative, please consult a doctor regarding this. 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.
Hope this helps. Take care!