Is the questioner's not being married and her illness, for which no medical diagnosis can be found, caused by magic?

If doctors cannot find a medical reason for infertility, it might be due to magic (sihr). The best cure for magic and other ailments is to seek refuge in Allah through supplication (du'a), to be diligent in acts of obedience, to recite the morning and evening remembrances (adhkar), and to perform ruqyah al-shar'iyyah (Islamic exorcism).

As for delaying marriage, it is a matter of divine decree. One should ask Allah to facilitate a righteous husband and seek help from trustworthy relatives and friends. It is permissible for a Muslim woman to seek a husband and offer herself for marriage.