What is the cause of the discharge of a brown substance for five days, accompanied by back and abdominal pain, after intercourse on the 14th and 15th days of the menstrual cycle, which is usually regular? Is this considered a normal period or a miscarriage? And what should be done?

The substance referred to is al-kudrah (a brownish or yellowish discharge). Its ruling is that it is not considered menses (hayd) unless it occurs during the accustomed period or comes immediately connected to blood. So, if a woman experiences it during her accustomed period or connected to blood, then it is menses, and she must abstain from everything a menstruating woman abstains from, and intercourse is not permissible during it. However, if it is not during her accustomed period and not connected to blood, then it is not menses.