Fertility is often taken for granted. Many factors can pose a hurdle to conception. Logically if we trace the events that lead up to conception it is not difficult to guess what those might be.
Irregular or Lack of ovulation. The most common cause of this is Polycystic ovary syndrome. Also hormonal imbalance in Thyroid and Prolactin hormones.
Decrease in the number and/or quality of eggs due to age/disease
Abnormalities of the uterus
Diseases that cause damage to ovaries/tubes/distort anatomy such as Endometriosis
When you see your doctor a detailed history and a thorough evaluation is done to find the contributory factors. Depending on the underlying cause, the management is planned to optimise your chances of conception.