Hi, A.,
The only thing I can say with any certainty is that, while you and your doctor are figuring out what is going on, you need to supplement with iron. Just adding more iron-rich foods to your diet probably won't suffice with this long-term blood loss going on. I'm using chlorophyll for my pregnancy anemia, which, unlike most iron supplements, doesn't cause constipation.
Iron deficiency can show up in the form of weakness and fatigue (hard to distinguish from being a new mom!), and, more specifically, pale or even bluish or greenish skin and light blue fingernails when resting (they might pink up with even light flexing, etc.). Also, you might be experiencing occasional dizziness, rapid/hard pulse, and palpitations. Sometimes people don't run into symptoms at all till they really start to crash.
It might be that you had a placental abruption that went unnoticed and is like a cut that never scabs. That is the only thing I can think of.
You might want to consult with a midwife. They know a lot of things that the doctors don't, and might be able to help you resolve the problem without getting a hysterectomy or other invasive procedure that has life-long consequences. I have found my midwives, and the ones whose books I've read, to be so knowledgeable, that from now on I will always take any of my reproductive health issues to THEM.
I hope your doctor warned you not to take asprin? Also, avoid flaxseed/oil, cod liver oil, fish oil supplements, and other things that thin your blood and increase your blood loss (or may even be the cause!). Check all of your supplements to see if they can cause this, too.
Take good care of yourself.
L.