heavy periods 2 weeks apart

My husband and I have been ttc for almost 4 years now. We have a daughter together who recently turned 7. She is perfect, happy and healthy. And as far as we know, so are we. So I have had, for the most part, pretty regular cycles. High normally range from 28 to 29 days apart. I just experienced 2 full heavy painful periods within 14 days apart. What does this mean? Should I be as worried about this as I am? Has anyone ever experienced this before? Could it just be stress? Could it be a miscarriage? Help!