I would echo what others have said, any bleeding that is abnormal for you, should be checked out.
I started on HRT about 9 months ago and would have long periods too, after getting the all clear that there was nothing else going on, a new doctor I saw said she thought I had too much progesterone in my body as I was also still on the mini pill (POP), I stopped the pill and things are starting to settle down, I've had periods but they've been 4-5 days max. The blood test I had at the time also confirmed I had way too much progesterone in my body.