Me!! I've had this for many many years since I was in my late teens .
To give you a bit of history I'm 28 ttc for 4 years now, I am certain this has to do something with my infertility.
I had a surgery in 2018 to remove endometriosis, wedge resection for ovarian cysts, endometrial erosion which someone else mentioned, polyps, all of these were "taken care of" and bleeding still continues.
Its not normal I know bc it's not just a pinch of blood ,its filling a pantiliner for 3 days . Some months worse than others.
I have done tremendous amount of research and currently ,after seeing many many doctors, I've started going to a naturopath to look for an alternative answer. She confirmed all the research that I've done basically
My bleeding tends to happen before the egg is release..
There is some research out there that says it's due to a sudden drop in estrogen when the egg is about to be released my naturopath explained qe should not be going through this it's a hormonal imbalance and were working to find the main cause
But so far she knows stress is a factor , i have stressful jobs ...also happends when i I excercise which is physical stress and also toxins and not the best diet..and imbalance of my thyroid , and overload of toxins through the enviroment/water ect
She put me on a supplement regimen along with dietary changes which I will follow for 3 weeks then have a follow up visit 
I'm really hoping this is it because this is frustrating specially when we are ttc
It's really hard to find people that are experiencing the same thing though
so of you wanna chat about it I'm here!