I think you are describing a normal occurrence for me! Since menstruation is the shedding of tissues from the lining of the uterus, it's totally normal to have 'clots.' It's just the tissues detaching from the wall of the uterus. Have your periods become heavier? That could explain the extra pain. This could just be a natural shift in your normal cycle which can happen with age.
I'm definitely not a physician, just a fellow female. I would really recommend seeing your OBGYN if it's still concerning you.