It is an unfortunate fact that changing lifestyles, high stress levels, late marriages and poor dietary habits have caused many couples to experience the frustration of childlessness. Some other biological reasons why you may not be able to conceive are:
Female Problems:
Irregular periods
Absence of periods
Polycystic Ovary Syndrome (PCOS)
Hormonal imbalance
PID (Pelvic Inflammatory Disease)
Age above 30
Thyroid disorders
Blocked fallopian tubes
History of miscarriages
Male Problems:
Quantity and quality of sperms
Erectile Dysfunction (ED)
Age above 30
Stress / prolonged mental tension
Sexually Transmitted Diseases (STDs)
Injury to the sex organs