really heavy periods?

i’m 15 and my periods are so heavy and painful, i normally have to have days off of school during my period. it’s really annoying this week because i have my mock exams and i have to be sat in exam conditions for up to 2 hours at a time (i usually change my pad every half an hour), so i cant stay off school, and i also can’t put in tampons so i’m at a loss with what i should do. does anyone know ways to ease pain (stomach and lower back) or make periods lighter somehow?