Dark spotting day 7-11 of cycle

[cwhiticker]

Hi Lara,
I've read your book the hormone repair manual, thank you. I learned more from that book than I have from any medical professional.
I am 38 and having surgery tomorrow to remove a polyp. I also have adenomyosis and PCOS (suspected inflammatory). I have had twins and one child prior conceived naturally (4 and 6). I am of normal weight/low weight, exercise regularly. I have recently cut out cow's milk. I do not have insulin resistance or thyroid issues.
The gyno and GP believe my mid cycle spotting is occurring due to adenomyosis and now the polyp. I don't believe this is the case as I have tracked it for 2 years and it always occurs on day 6 or 7 and lasts 4-5 days. It is very dark sometime black spotting that occurs at this time. My cycles are irregular and over 30 days.
Would you recommend I take Prometrium 100-200mg in the luteal phase? I can't work out what my hormone imbalance would be and both health care providers recommend I try the mirena again (I disliked it and had it removed after 8 months in October last year). I don't require contraception.