In male, systematic diseases like diabetes and obesity; endocrine disorders like pituitary infantilism, hypothyroidism, adrenal hyperplasia are important causes. Similarly factors like heavy smoking, alcoholism, nervous tension about sex, and psychological problems can also be responsible. Genital factors like defective spermatogenesis, testicular atrophy following mumps; infections like gonococcal and tubercular in the genital tract, and aging above 45 can cause this disorder.

In Female, systematic diseases sufficient to suppress the ovulation and age above 40 are very common causes. Endocrine factors like frohlich’s syndrome, psychological factors like fear, and nervousness can also cause this problem. Genital factors like narrow vaginal introitus, vaginal atresia, high vaginal acidity, cervical, uterine, tubal, and ovarian disorders can cause sterility in females. Also, STD's can contribute to infertility, such as chlamydia. This results in pelvic inflammatory disease, which scars the fallopian tubes and prevents the egg from being fertilized.

There are too many causes to list. If you have regular periods and no other signs of reproductive disease, you need to have a pelvic exam done as well as a few hormone levels run first to rule out physical problems. Sometimes, no matter how healthy we are, nature isn't agreeable to impregnation. By the way, I know numerous people, myself included, who just stopped trying to get pregnant and then did! Good luck.