hi there--
what my ob/gyn told me when i was discussing iuds what that the copper one, while having no hormones (yay!) would possibly lead to heavier, "worse" periods (boo!). i went with the mirena iud since, while it has a little hormone (much less than the pill), my periods would be lighter and easier. i am very happy with the mirena. i get a little pms (a little moody, maybe a little headache) but not like on the pill (3 days of bloatedness, headache, rage ;)), and no cramps. plus i only need a liner for a couple days as opposed to the week-long bleeding on the pill. very light period which only really comes due to acupuncture and my body regulating that way.
i agree with the other poster that changing a tampon every hour is something to check with your doctor about. if you can, maybe look into acupuncture-- it really helps me with a host of things. also, exercising helped me with pms and period symptoms.
good luck!