I am dealing with something similar.I had heavy 3 week periods for three years and they could not figure out what was going on.Nothing they tried would stop the bleeding.I got a one time 1020 mg iron infusion and the periods stopped for almost a year, but I am still showing low iron.I have gone to so many Gynocologists and GI doctors and they can't find a thing.I am thinking it might be something they are not seeing in the intestines.Have you been checked for sibo in your gut?I was doing some research and saw that sibo can deplete you of Iron and B12.