menstrual cycle problems

My sister is 21 years old and when she gets her cycle she gets extremely bad cramps in her legs. Can't walk, vomits or most of the day if she tries to take medicine. We have been to numerous doctors and they have not found anything. One doctor said she might have cysts on ovaries but couldn't find them. This was last year. And it has gotten worst. She is going to a doctor next week to see if they can find anything. But I also wanted to check here to see if anyone had any advice.

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