Black discharge & minimal flow in period

My wife suffers from endometriosis with cysts on both ovaries. We are trying for pregnancy. We did a course of letroze + duphaston and then letroz + clomid + gestofit sr 200. We were advised to stop medication from the last month and try for one more month. In this month's period, she had heavy dark red flow and severe pain on the first day, where she almost fainted. She was administered zylpan 40 mg + venflon 20 + pan d + cyclopam and other painkillers to reduce the pain. After pain relieving, for the next two days, she has negligible flow with black pieces of blood being discharged. I understand the black pieces are old blood, but why has the flow almost non-existent is it due to the side effects of medicine or something else? Kindly advise. Today is the fourth day and no flow/discharge till now.