Could you be having a miscarriage? Also sometimes as you get older your body changes. I've had that before myself. When my periods are usually light too. If you can fill a pad every hour, you should see a dr.
I'm not a doctor but over the years i have had many heavy periods with clots and i've been fine. If the bleeding continues for more than 7 days I would see a doctor and if the pain lasts for more than 48 hrs I would see the doctor or go to the hospital. Hope you are OK.