Painful Bump on Outer Labia (Labial Cyst), not STD

Im looking for information/advice about Labial Cysts and if anyone knows how or why they develop? There is very little information online... and so much of it points to STDs - this is not.

Im 42, clean, have good vaginal health, regular cycles and have never ever had this issue until this year. I have been seen by 3 ObGyn doctors and 1 STD clinic to make sure it's nothing else. Its not thankfully, but still quite annoying. Its also NOT a Bartholin Cyst (it changes locations and sides, not just where the Bartholins gland is).

It seems to appear every third month approximately. My doctor is not concerned, says it's quite normal - but I'd like to know if it's something causing it, so I can stop or adjust what Im doing to prevent them in future, as they are tender and a bit painful. Its about the size of a pea, firm and just under the skin

Anyone else go through this? Any tips or advice?

I thought of posting a picture, but really don't think that will help much... and know Im not a fan of those shots myself 😕

Thank you in advance!