Need some answers!!

Need some insight. I have a friend that gets her period twice a year at most, very painful last 1-2 weeks this month her bleeding comes for an hour then stops and starts again about every two hours. She does get normal periods when on bc but it makes her extremely moody. She thought pcos but really no other symptoms besides the very irregular periods. What could this possibly be anyone experience this or know someone who has? Need all the suggestions!!