As I said, I wouldn’t necessarily recommend the mirena either as any IUD can make the pain worse.
It’s really hard to recommend anything just from your description. As I said, it depends on what causes the pain. It you’re comfortable with it, you could start taking a combined pill again in in a 3-month cycle (usually they recommend Valette or Maxim for that, but you can do it with any pill, so maybe one with a lower dosage of hormones would work too, such as Belara/Mona Hexal 20). You should definitely consider seeing an endometriosis specialist soon though, as taking a pill that contains estrogen can make it worse.
If it’s not endometriosis, taking a combined pill in a 3-month-cycle would probably be the way to go.
And as I said; Supplementing magnesium is never a bad idea when you have bad menstrual cramps.
And I guessed you’re from Germany because your gynecologist-story sounds strikingly similar to my own.
Btw since you are from Germany: Look up on https://mezis.de/
if there’s a gyno listed anywhere near you. It’s really, really hard to find one ‘out in the wild’ whose treatment isn’t affected by what’s most profitable for them.