Just to make you feel better - I googled and the thing you're seeing about over 5mm being worrying is only for post-menopausal women. This is what I found regarding people who still menstrate:

In premenopausal patients, there is significant variation at different stages of the menstrual cycle.

  • during menstruation: 2-4 mm
  • early proliferative phase (day 6-14): 5-7 mm
  • late proliferative / preovulatory phase: up to 11 mm
  • secretory phase: 7-16 mm <-- this would be where you are if you're almost to your period. So, totally normal.

That said, doctors in my experience are so dismissive of women's pain. Even though it's nothing sinister I would still persist in finding a cause so you can stop being in pain!