Hi Nas!
Another cause of postmeno bleeding on continuous combined MHT is a high progestogen-to-estrogen ratio, ie not enough estrogen. That was my problem. I wasn't absorbing the patch.
I started MHT, Estradot 50 and Prometrium/Utro 100 mg, in Feb 2020. Bleeding started a few weeks later and continued. In Sep/Oct 2020, a transvaginal ultrasound and sonohysterogram found no abnormalities. Biopsy negative. Endometrium was 1 mm.
Bleeding became heavier and more frequent, every 10-14 days. Even with my thin endometrium, my doctor didn't consider low estrogen as a possible cause for the bleeding. He suggested reducing my estrogen or fitting a Mirena.
My symptoms worsened and the bleeding increased. I frequently had to use a tampon at night. The constant bleeding made it difficult to treat VVA/GSM. In Sept 2021, my doctor finally ordered blood tests which confirmed low estrogen. It was so low, a precise measurement couldn't be provided on the report. With that info, he concluded the bleeding was due to the progesterone and I was switched to oral estrogen.
Excessive progestogen may produce bleeding from an atrophic endometrium. It's another cause of postmeno bleeding on continuous combined MHT that isn't discussed much. Even my doctor didn't consider it for a long time.
Now that I'm on oral estrogen, my bleeding has been steadily lessening, spotting as opposed to bleeding. Early days. Hoping it resolves with time. It's so difficult to find the right balance and this trial-and-error approach to hormone therapy is wearying. With the continued bleeding, I wonder if something was missed on the scans. It's such a worry. I can understand why so many women give up on MHT. But I'm finally through the worst of the temp side effects of the new regimen and feeling some benefit, so onwards I will go.
Looking forward to hearing how others resolve their bleeding.