Hemorrhoids(piles), caused due to congestion in vessels that supply blood to anus due to pressure on vessels..they r of 2 types in ternal hemorrhoids n external..internal hemorrhoids r common n bleeds but pain will be rare, external hemorrhoids rarely bleeds but cause more pain.. comming to your question due to hormonal changes dat causes constipation during periods, (hormones relaxes muscles of colon) during constipation it exerts more pressure on vessels on told above which can be minimised by taking fibre food r laxatives.periods just aggrevates periods, whic can be prevented..personal hygiene also plays imp role.. if external piles associated with more pain then consult surgeon.. Thanq.