Is the intermittent blood that continues for more than ten days after childbirth, interspersed with yellowish discharge, considered menstruation or postpartum bleeding (istihada)? And is there any medicine to stop this spotting?

This blood in question is menstrual blood because it appeared during a time suitable for menstruation, as it was preceded by a period of purity exceeding fifteen days, and its duration did not exceed fifteen days. The yellowish discharge connected to this blood is considered menstruation. If you become pure before the lapse of fifteen days, then this entire period is menstruation. If the duration of the blood and the yellowish discharge connected to it exceeds fifteen days, then you are experiencing irregular bleeding (istihada).