How To Reduce Menstrual Pain?

Hi.Im 18 years old.my period started when I was 13.I can t do anything because of the extreme pain.I also go through problems like loose motion and gas during my period.Im lactose intolerant so at first I used to think that maybe it s because I ate sth last week..and its acting up now.But even if I don t eat anything that has milk in eat I get loose motion.my periods are 6-8 days long.and I suffer badly in the first few days.My board exams start in April.Im really worried about my studies as I cant concentrate with the pain.PLEASE HELP!