I had retained products which were finally taken out with a sweep when I was about 6 weeks post partum.
If I were you, I would book myself an appointment with another obgyn (ask around if you can and find one other women recommend). I would pay for it myself if necessary (and possible within your budget). I would save for and prioritise that appointment over anything else too - this is your health.
I say this because when I was discharged after my first (horrendous) birth, I had extremely heavy bleeding, enough for me to call the emergency line. They told me it was normal. I couldn't walk without pain, was exhausted. Still told it was normal. Eventually I went back to my (ex) ob (long story - I got to see her because she listened to my husband, not me - will never forgive her for that) and turned out I had retained products that needed to be removed. I was lucky I didn't get a rip-roaring infection.
Anyway, if you are in pain, there is a reason. someone needs to explain to you that reason. a mid wife saying "nothing we can do" is not sufficient. The answer to that is fine, I will go to someone who has the skill to actually do something.
I probably sound a bit strident but I do think women's health issues, in particular lingering pain/discomfort/issues after childbirth are minimised in a way that other health issue are not. You may be experiencing this. I think you should find someone who will actually diagnose and treat you ... like a medical professional is supposed to do.