menstrual cycle period

Hi, my daughter is 13 years old and has been getting constant stomach pains for nearly 2 years, it all started when she had her apendix out. We kept going back to the hospital and doctor appt and they  all have difftrent opinons. they are saying  that it is chronic pain but they also found a cyst and said that it had fallen off.her period have gone for 5 days to 1 and a half days,  also when she gets  her period it has little clots in the blood . she  gets very sick around the time of her periods and vomits up to 10 times a day after her periods but the doctors say it normal have you got any ideas what it could be or what could make the pain stop