What Causes Stomach Cramps And Vaginal Bleeding While On Apri 28?

I am on my 3rd week of Apri 28 day and have been feeling horrible. I have horrible cramps, have been lightly bleeding since I started and seem to be more tired. I started this medicine because I would have extremely painful, debilitating and heavy but short periods for years. I just had a pap test and the doctor said she didn't see anything that would be cuaseing that. I'm wondering if the pain is normal for this medicine and if I should get another opinion on why my periods are so horrible.