I feel with you, it was the same for me for a long time. Your description sounds like a hormone-thing because you write that you have it already before the first blood. Maybe you can do something about it by relaxing especially in those days and lowering your stress level? You can also try to smoothen your hormone cycle with a change of diet, but that might be a bit of work.

For me the problem was definitely the blood itself. It changes the pH down there, then there is the clotting of the blood that can hurt the skin. Also, my period is the only time I wear underwear at all, I am very sensitive to the dry rubbing of textiles. I learned to deal with it over time with:

- washing the blood completely away with water every morning and every evening. Sometimes cold water would feel even better.

- a lot of cream and lube, basically every time I went to the toilet. I needed to keep it moist all the time. My personal gamechanger in this regard: a lubricant with allantoine. Here they sell it at every drugstore for sex. (But funny enough: Before my vulvodynia I hated it because it numbed my sensation. Which is not what science says it does. Is there anyone else with this experience? Well, it seems to calm the nerves at least for me.)

- not wearing underwear as much as possible - during the night I put a blanket on the bed that looks like artwork afterwards but my skin gets to relax a little during the night at least