Heavy Flow

Soooo my periods are usually super heavy & lasts at least 5 days. I use Kotex super plus tampons & still go through like 5+ a day. Is this normal? Sometimes I get low iron & feel dizzy from losing so much blood. My cramps are also really terrible sometimes I feel like I can't even get out of bed. My doctors told me it was normal as long as my iron isn't dangerously low but it's always low when I get it checked. Is there anything I can do to stop the super bad cramps & feeling dizzy or to make my periods lighter?