I have the same problem too for almost a year, it's better to see ec because when I told my ec about this and he said the egg is damage so it's bleeding. It causes defect so it's hard to get pregnant. If it keeps happening months and months, go to see ec ! Anyway, if your inside condition is good, it won't bleed. I didn't notice that and I think it is normal until I see this ec last month. My last cycle is getting much more better, I used to have 2 sometimes 3 days bleeding during 排卵期.